[ResponseOps][Window Maintenance] Add window maintenance to alerting plugin public folder and add create form

[doakalexi]

Resolves #152272

Summary

• This PR adds maintenance windows to the alerting plugin and also adds the create form.
• The Maintenance Windows feature is hidden by a feature flag by default.
• The create form calls the create api, but it's expected to fail because the api hasn't been merged.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Unit or functional tests were updated or added to match the most common scenarios

To verify

• Enable maintenance windows by adding ENABLE_MAINTENANCE_WINDOWS = true to x-pack/plugins/alerting/common/index.ts
• Go to http://localhost:5601/app/management/insightsAndAlerting/maintenanceWindows or select the Maintenance Windows link on the side nav
• Click the Create a maintenance window button and verify it takes you to the create from
• Verify the bread crumbs and the return link work correctly
• Once on the create form, try to submit without entering any values and verify that the form doesn't submit and errors are shown on the name and duration fields
• Submit a maintenance window that is not recurring. You'll see an error popup but verify that the request body is correct and matches what you've selected in the form.
• Create a maintenance window that is recurring and try choosing the different options on the recurring form. Verify that the summary at the bottom of the form accurately reflects what you have selected.
• Submit a maintenance window that is recurring. Again, you'll see an error popup but verify that the request body is correct and matches what you've selected in the form.

[lcawl]

UI text LGTM, thanks!

[mdefazio]

LGTM!

[JiaweiWu]

Just a few last comments, but otherwise LGTM!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: cbb2919

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
alerting	35	78	+43

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
alerting	550	551	+1

Async chunks

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

id	before	after	diff
alerting	0.0B	152.3KB	+152.3KB

Page load bundle

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

id	before	after	diff
alerting	44.6KB	47.9KB	+3.4KB

Unknown metric groups

API count

id	before	after	diff
alerting	571	572	+1

async chunk count

id	before	after	diff
alerting	0	4	+4

ESLint disabled in files

id	before	after	diff
alerting	1	2	+1

ESLint disabled line counts

id	before	after	diff
alerting	80	82	+2
securitySolution	433	436	+3
total			+5

Total ESLint disabled count

id	before	after	diff
alerting	81	84	+3
securitySolution	512	515	+3
total			+6

History

• 💚 Build #118973 succeeded 5936064
• 💔 Build #118720 failed 74d759f
• 💔 Build #118660 failed e5d8d89
• 💔 Build #118637 failed 740d17c
• 💚 Build #118036 succeeded 30c30c7
• 💛 Build #117773 was flaky 39f0a74

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@elasticmachine merge upstream