feat: CI/CD improvements - Consider implementing yamllint

[javydekoning]

Some examples have inconsistent indentation. For example:

https://github.com/awslabs/aws-deployment-framework/blob/master/samples/sample-ecs-cluster/template.yml#L8-L13

Others like the below have incorrect syntax:

aws-deployment-framework/src/lambda_codebase/initial_commit/bootstrap_repository/example-adfconfig.yml

Lines 18 to 20 in cdfa538

	scm: # Source control management
	auto-create-repositories: enabled # If true and using CodeCommit as source, the repository will be automatically created
	default-scm-branch: master # The default branch is used when the pipeline does not specify a specific branch. If this parameter is not specified, it defaults to the "master" branch.

auto-create-repositories should be a property of scm: hence needs to be indented.

To start I'm proposing to implement yamllint with the following .yamllint config file:

---
yaml-files:
  - '*.yaml'
  - '*.yml'
  - '.yamllint'

rules:
  braces: enable
  brackets: enable
  colons: enable
  commas: enable
  comments:
    level: warning
  comments-indentation:
    level: warning
  document-end: disable
  document-start: disable
  empty-lines: enable
  empty-values: disable
  hyphens: enable
  indentation: enable
  key-duplicates: enable
  key-ordering: disable
  line-length: disable
  new-line-at-end-of-file: disable
  new-lines: enable
  octal-values: disable
  quoted-strings: disable
  trailing-spaces: enable
  truthy:
    level: warning

This should catch the above syntax error and improve overall code consistency.