[21286] Improve CI workflows in master (backport #216)

[mergify]

Description

This PR improves the CI workflows, making them as similar as possible to the Fast DDS workflows.
It also introduces a braching model refactor, similiar as the performed in Fast DDS repository.

It is on top of (and must be merged after) this PR:

• [20414] Add PR template  #203

Note: While backporting this PR, please ensure the following changes:

• Remove nightly jobs
• Update ubuntu-ci.yml, mac-ci.yml and windows-ci.yml files with the proper fallback branches
• Maintain reduced version of the RELEASE_SUPPORT.md (only reference to master links)
• Create mirror job on 1.1.x brach (targetting 1.x)
• Fast CDR 1.0.x requires building on ubuntu-20.04

@Mergifyio backport 2.2.x 1.1.x 1.0.x

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A The code follows the style guidelines of this project.
• N/A Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A Any new/modified methods have been properly documented using Doxygen.
• N/A Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• N/A Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: CI pass and failing tests are unrelated with the changes.

---

This is an automatic backport of pull request #216 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 203725d has failed:

On branch mergify/bp/1.1.x/pr-216
Your branch is up to date with 'origin/1.1.x'.

You are currently cherry-picking commit 203725d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   .github/workflows/config/test.meta
	new file:   .github/workflows/config/test.repos
	new file:   .github/workflows/mac-ci.yml
	new file:   .github/workflows/nightly-mac-ci.yml
	new file:   .github/workflows/nightly-ubuntu-ci.yml
	new file:   .github/workflows/nightly-windows-ci.yml
	new file:   .github/workflows/reusable-ci.yml
	new file:   .github/workflows/ubuntu-ci.yml
	new file:   .github/workflows/windows-ci.yml
	modified:   README.md
	new file:   RELEASE_SUPPORT.md

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/pull_request_template.md
	deleted by us:   .github/workflows/config/build.meta
	deleted by them: .github/workflows/fastcdr-test.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[JesusPoderoso]

LGTM with green CI