[Cases] Use the bulk create attachment endpoint on the UI

[cnasikas]

Fix mapping## Summary

This PR changes the UI to use the new bulk create attachment internal API.

Depends on: #129092

Checklist

Delete any items that are not applicable to this PR.

• Unit or functional tests were updated or added to match the most common scenarios

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[elasticmachine]

Pinging @elastic/response-ops-cases (Feature:Cases)

[academo]

I really liked how you made the change to be a drop-in replacement. Only missing a small validation to prevent a wrong API call.

Something I'd like to change but you don't have to because it will be a lot of work, is to remove the "bulk" from the name to simply createAttachments as the name already implies plural.

If you feel like doing it, go for it, but I won't hold the PR for that.

[academo]

Thanks for the renaming!

[kibana-ci]

💛 Build succeeded, but was flaky

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• Commit: c8ff8a9
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Test Failures

• [job] [logs] Cases Cypress Tests on Security Solution / Alerts timeline Privileges: can crud should allow a user with crud privileges to attach alerts to cases

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
cases	283.8KB	283.8KB	+7.0B

Page load bundle

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

id	before	after	diff
cases	90.7KB	90.7KB	+86.0B

History

• 💛 Build #38136 was flaky 1016c45
• 💚 Build #37929 succeeded f4c556922259394ae668d38a5611f91de39e6ca8

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

cc @cnasikas