feat: export relation between experiment and container to metrics

[kaaass]

What problem does this PR solve?

RFC: chaos-mesh/rfcs#47

This PR implements the feature of exporting relation metrics in RFC. Relation metrics are the metrics that describe the relation between the Chaos experiment and the container. These metrics are exported by Chaos Controller Manager. The proposed metric name is: chaos_controller_manager_chaos_experiments_container_relation. It is exported with the following labels:

Label Name	Description
namespace	The namespace of the container.
kind	The kind of the experiment.
phase	The phase of the experiment. No longer export this because of confusion.
name	The name of the experiment.
uid	The UID of the experiment.
pod	The pod name of the selected container.
container	The container name of the selected container.

The relation metrics are exported for all Chaos experiments managed by Chaos Controller Manager if the phase of the experiment is not Finished or Deleting. This prevents exporting too many metrics by ignoring inactive experiments.

For each selected container in the experiment, Chaos Controller Manager exports a relation metric. The value of the metric is always fixed to 1 for the convenience of joining metrics.

What's changed and how it works?

Proposal: chaos-mesh/rfcs#47

This PR modifies Chaos Controller Manager by exporting new metrics to /metric endpoint. The relationship between the experiment and the selected container is extracted through the status records of Chaos Object.

Related changes

• This change also requires further updates to the website (e.g. docs)
• This change also requires further updates to the UI interface

Cherry-pick to release branches (optional)

This PR should be cherry-picked to the following release branches:

• release-2.6
• release-2.5

Checklist

CHANGELOG

Must include at least one of them.

• I have updated the CHANGELOG.md
• I have labeled this PR with "no-need-update-changelog"

Tests

Must include at least one of them.

• Unit test
• E2E test
• Manual test

Side effects

• Breaking backward compatibility

DCO

If you find the DCO check fails, please run commands like below (Depends on the actual situations. For example, if the failed commit isn't the most recent) to fix it:

git commit --amend --signoff
git push --force