[8.x] [Dashboards] Add getSerializedState method to Dashboard API (#204140)

[nickpeihl]

Backport

This will backport the following commits from main to 8.x:

• [Dashboards] Add getSerializedState method to Dashboard API (#204140)

Questions ?

Please refer to the Backport tool documentation

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 776d28f

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
dashboard	689	690	+1

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
dashboard	111	113	+2

Async chunks

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

id	before	after	diff
dashboard	632.7KB	633.0KB	+337.0B

Unknown metric groups

API count

id	before	after	diff
dashboard	114	117	+3