Update go client README to match modern module support (#23292)

* Update go README to match modern module support

Updated go client installation instructions to use go modules explicitly.

* regenerate examples

Author: deltamualpha

modules/openapi-generator/src/main/resources/go/README.mustache

@@ -20,17 +20,7 @@ For more information, please visit [{{{infoUrl}}}]({{{infoUrl}}})
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-{{#hasOAuthMethods}}
-go get golang.org/x/oauth2
-{{/hasOAuthMethods}}
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import {{packageName}} "{{gitHost}}/{{gitUserId}}/{{gitRepoId}}{{#isGoSubmodule}}/{{packageName}}{{/isGoSubmodule}}"

samples/client/echo_api/go-external-refs/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import openapi "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/client/echo_api/go/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import openapi "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/client/others/go/allof_multiple_ref_and_discriminator/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import openapi "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/client/others/go/oneof-anyof-required/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import openapi "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/client/others/go/oneof-discriminator-lookup/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import openapi "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/client/petstore/go/go-petstore/README.md

@@ -12,15 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/oauth2
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import petstore "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/openapi3/client/extensions/x-auth-id-alias/go-experimental/README.md

@@ -12,14 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import x_auth_id_alias "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/openapi3/client/petstore/go-petstore-generateMarshalJSON-false/README.md

@@ -12,15 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/oauth2
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import petstore "github.com/GIT_USER_ID/GIT_REPO_ID"

samples/openapi3/client/petstore/go-petstore-withXml/README.md

@@ -12,15 +12,7 @@ This API client was generated by the [OpenAPI Generator](https://openapi-generat
 
 ## Installation
 
-Install the following dependencies:
-
-```sh
-go get github.com/stretchr/testify/assert
-go get golang.org/x/oauth2
-go get golang.org/x/net/context
-```
-
-Put the package under your project folder and add the following in import:
+Import the package in a go file in your project and run `go mod tidy`:
 
 ```go
 import petstore "github.com/GIT_USER_ID/GIT_REPO_ID"