Cherry-pick #25193 to 7.x: Proxy processes/elastic-agent to stats

[michalpristas]

Cherry-pick of PR #25193 to 7.x branch. Original message:

What does this PR do?

This PRs just make proxies processes/elastic-agent to /stats so metricbeat configuration on cloud can be a bit more simple

Why is it important?

readability/usability on cloud side

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.

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Build Cause: Pull request #25197 opened

• Start Time: 2021-04-21T11:32:43.859+0000

• Duration: 58 min 14 sec

• Commit: d8aad32

Test stats 🧪

Test	Results
Failed	0
Passed	6740
Skipped	24
Total	6764

Trends 🧪

💚 Flaky test report

Tests succeeded.

Expand to view the summary

Test stats 🧪

Test	Results
Failed	0
Passed	6740
Skipped	24
Total	6764