[7.11] [ML] Support legacy watcher URL (#86661)

[darnautov]

Backports the following commits to 7.11:

• [ML] Support legacy watcher URL ([ML] Support legacy watcher URL #86661)

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: a7ce356

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
ml	7.0MB	7.0MB	+1.7KB
triggersActionsUi	1.5MB	1.5MB	-26.9KB
total			-25.1KB

Distributable file count

id	before	after	diff
default	47626	48389	+763

Page load bundle

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

id	before	after	diff
triggersActionsUi	162.0KB	162.1KB	+102.0B

Unknown metric groups

async chunk count

id	before	after	diff
triggersActionsUi	31	32	+1

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream