Moved Deploy template content into its own Kubernetes yaml

What does this MR do?

This MR splits the current Deploy.gitlab-ci.yml template into new Kubernetes.gitlab-ci.yml and ECS.gitlab-ci.yml templates.

As a result of doing this split, we need to have the means to decide which type of deployment the pipeline should perform. To do so, there are some rules to keep in mind, based on the issue proposal:

• We need to make sure that if the user is using Kubernetes - the regular auto DevOps template is initiated.
• If a user is not using Kubernetes, and is deploying to AWS, this new auto-deploy-to-ECS is initiated
• If a user is not using Kubernetes and not using AWS, both templates are skipped
• If a user is using Kubernetes and deploying to AWS - Only run the deploy Kubernetes template

To make these choices, we can definitely leverage the existing kubernetes: active attribute and we can also introduce the new AUTO_DEVOPS_PLATFORM_TARGET CI variable for that purpose.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #208132 (closed)