Global processors reload

[pchila]

Proposed commit message

This PR attempts to load global processor configuration from the control protocol to allow for some control when running under elastic-agent.

Please have a look at elastic/elastic-agent-client#117 and elastic/elastic-agent#5052 for the client and elastic-agent changes respectively.

In this PR I added:

• a tracking of the clients connected to the pipeline object
• a reload mechanism for the global processor configuration

What is still missing:

• a proper way of pausing the processing for a moment and perform a call on each pipeline client to set the new global processor on each

This PR has been on hold as the solution look a bit too complicated and there are risks of deadlocks (think about Pipeline trying to set processor on a client that is trying to publish on the same Pipeline) and a different approach has been drafted in another PR based on this one

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.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates Allow disabling and configuring the add_x_metadata default global processors elastic-agent#4670

Use cases

Screenshots

Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @pchila? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit