chore: remove note of go being in dev preview (#21130)

Removes note in go app init template readmes saying go is in dev preview
since it is not generally available. Also adds note about `cdk.json` which may
be useful for new users and is present in other language templates.

references: awsdocs/aws-cdk-guide#416


----

### All Submissions:

* [X] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/init-templates/app/go/README.md

@@ -2,9 +2,7 @@
 
 This is a blank project for CDK development with Go.
 
-**NOTICE**: Go support is still in Developer Preview. This implies that APIs may
-change while we address early feedback from the community. We would love to hear
-about your experience through GitHub issues.
+The `cdk.json` file tells the CDK toolkit how to execute your app.
 
 ## Useful commands
 

packages/aws-cdk/lib/init-templates/sample-app/go/README.md

@@ -2,9 +2,7 @@
 
 This is a blank project for Go development with CDK.
 
-**NOTICE**: Go support is still in Developer Preview. This implies that APIs may
-change while we address early feedback from the community. We would love to hear
-about your experience through GitHub issues.
+The `cdk.json` file tells the CDK Toolkit how to execute your app.
 
 ## Useful commands