[7.x] [ML] add marker body (#104672)

[kibanamachine]

Backports the following commits to 7.x:

• [ML] add marker body ([ML] Fix date marker formatting in revert model snapshot flyout #104672)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: cf66a67
• Storybooks Preview

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	5.9MB	5.9MB	+19.0B

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

cc @darnautov