Create separate documentation.yaml file

[RedbackThomson]

Closes aws-controllers-k8s/community#1223
Expands upon #394

Description of changes:
This pull request moves the custom GoDoc overrides from inside the generator.yaml file to a new, separate documentation.yaml file. This documentation.yaml file currently supports modify field GoDocs (but could be extended to modify resource GoDocs as well) in the following ways:

• Prepend: Add a comment before the existing shape ref GoDoc
• Append: Add a comment after the existing shape ref GoDoc
• Override: Completely replace the existing shape ref GoDoc

The current RDS documentation modifications are now modeled in the documentation.yaml like so:

resources:
  DBClusterParameterGroup:
    fields:
      Parameters: 
        override: |
          DEPRECATED - do not use.  Prefer ParameterOverrides instead.
      ParameterOverrides: 
        append: |
          These are ONLY user-defined parameter overrides for the
          DB cluster parameter group. This does not contain default or system
          parameters.
  DBParameterGroup:
    fields:
      ParameterOverrides: 
        append: |
          These are ONLY user-defined parameter overrides for the DB parameter
          group. This does not contain default or system parameters.

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

[jaypipes]

great stuff here @RedbackThomson! really appreciate this. Couple smallish nits inline but overall awesome.

[jaypipes]

Please add docstrings for these fields

[jaypipes]

Any reason you wanted to delete empty newlines? Sometimes a long docstring is better broken into paragraphs.

[RedbackThomson]

Only deleting trailing newlines here

[jaypipes]

@RedbackThomson also, see unit test output failure:

 	want (*model.SDKAPI, string, string, "github.com/aws-controllers-k8s/code-generator/pkg/config".Config, "github.com/aws-controllers-k8s/code-generator/pkg/config".DocumentationConfig)
# github.com/aws-controllers-k8s/code-generator/pkg/testutil [github.com/aws-controllers-k8s/code-generator/pkg/generate/ack.test]
pkg/testutil/schema_helper.go:91:73: not enough arguments in call to ackmodel.New
	have (*model.SDKAPI, string, string, "github.com/aws-controllers-k8s/code-generator/pkg/config".Config)
	want (*model.SDKAPI, string, string, "github.com/aws-controllers-k8s/code-generator/pkg/config".Config, "github.com/aws-controllers-k8s/code-generator/pkg/config".DocumentationConfig)
FAIL	github.com/aws-controllers-k8s/code-generator/pkg/generate/ack [build failed]
FAIL	github.com/aws-controllers-k8s/code-generator/pkg/generate/code [build failed]
?   	github.com/aws-controllers-k8s/code-generator/pkg/generate/crossplane	[no test files]
?   	github.com/aws-controllers-k8s/code-generator/pkg/generate/olm	[no test files]
?   	github.com/aws-controllers-k8s/code-generator/pkg/generate/templateset	[no test files]
?   	github.com/aws-controllers-k8s/code-generator/pkg/metadata	[no test files]
FAIL	github.com/aws-controllers-k8s/code-generator/pkg/model [build failed]
FAIL	github.com/aws-controllers-k8s/code-generator/pkg/model/multiversion [build failed]
ok  	github.com/aws-controllers-k8s/code-generator/pkg/sdk	0.319s
make: *** [Makefile:56: test] Error 2 

[a-hilaly]

/retest

[RedbackThomson]

@a-hilaly @jaypipes Unit tests passing + added code doc

[a-hilaly]

Nice, ty @RedbackThomson !
/lgtm

[RedbackThomson]

This will require a follow up with the RDS controller to move their stuff over. Reminder to me to do that

[a-hilaly]

/lgtm

[a-hilaly]

/lgtm

[ack-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: A-Hilaly, RedbackThomson

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[a-hilaly]

/retest