[8.18](backport #9082) deps: use the latest updatecli version and use oblt-actions

[mergify]

What does this PR do?

• Bump updatecli version to the latest available, so the latest updatecli policies work out of the box.

• Use oblt-actions for the Slack notifications and updatecli.

Why is it important?

#9067 was merged but introduced a hard dependency with the updatecli version, see https://github.com/updatecli/policies/blob/main/updatecli/policies/autodiscovery/updatecli/CHANGELOG.md#090

Simplify the usage of the Slack notifications using the existing wrapper.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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

In the CI only, see the below runs:

• updatecli-compose
• bump-elastic-stack-snapshot
• bump-golang
• update-beats - expected, it requires backports
• bump-vm-images - expected, it requires backports

Related issues

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 #9082 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 58886e6 has failed:

On branch mergify/bp/8.18/pr-9082
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit 58886e60c.
  (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/workflows/bump-vm-images.yml
	new file:   .updatecli-version

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/workflows/bump-beats-version.yml
	both modified:   .github/workflows/bump-golang.yml
	deleted by us:   .github/workflows/bump-otel-version.yml
	both modified:   .github/workflows/updatecli-compose.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

[v1v]

@elastic/observablt-dx, we need your help here - otherwise any CI running for elastic/elastic-agent on Saturdays might fail. 🙏

[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

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 1c327fa

cc @v1v