[9.0] [DOCS] Update URLs for apm, monitoring, and observability (#218030)

[lcawl]

Backport

This will backport the following commits from main to 9.0:

• [DOCS] Update URLs for apm, monitoring, and observability (#218030)

Questions ?

Please refer to the Backport tool documentation

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 8e9bfaf

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
aiAssistantManagementSelection	100.4KB	100.9KB	+489.0B
lists	144.3KB	144.8KB	+489.0B
total			+978.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
core	427.3KB	427.8KB	+489.0B