[8.14](backport #4836) [CI] Trigger improvements

[mergify]

What does this PR do?

Draft PRs will not run integration tests. If you need to run them use /test extended trigger comment.
Introducing skip-ci and skip-it labels.
Makes buildkite pull request builds to ignore .ci and .github directories.
Also all *.md files
Made file patterns more strict by adding ^
Added CI cheatsheet to pull request template

Why is it important?

Integration tests were executed

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

• Closes Skip integration tests for changes that do not modify Go source files #3674

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

---

This is an automatic backport of pull request #4836 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 0b99ccb has failed:

On branch mergify/bp/8.14/pr-4836
Your branch is up to date with 'origin/8.14'.

You are currently cherry-picking commit 0b99ccb922.
  (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:
	modified:   .github/PULL_REQUEST_TEMPLATE.md

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/pull-requests.json

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

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[mergify]

This pull request has not been merged yet. Could you please review and merge it @pazone? 🙏

[pierrehilbert]

@pazone what is the expected timeline with this PR?

[pazone]

I think it must be closed in favour to another PR