[Cases] Allow custom toast title and content in cases hooks

[academo]

Summary

Closes: #127968

Updated logic:

if any custom title or content is passed, those will display.
If at least one of the passed attachments is an alert, the toast will show an alert-specific message.
if none of the attachments are alerts, or no attachments are passed. The toast will show a "generic" updated title and no content.

For all cases the "view case" link will show.

[elasticmachine]

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

[elasticmachine]

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

[academo]

@elasticmachine merge upstream

[academo]

@elasticmachine merge upstream

[peteharverson]

LGTM

[cnasikas]

Tested and LGTM!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 040ca53
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• Webpack Bundle Analyzer

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	292.5KB	292.5KB	+4.0B

Page load bundle

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

id	before	after	diff
cases	85.1KB	85.9KB	+841.0B

History

• 💔 Build #33078 failed 356a7f1
• 💚 Build #33000 succeeded f682a6a
• 💚 Build #32507 succeeded d83d52a243072b63d3cf9fb2c3d3a57fb8f91258
• 💛 Build #32196 was flaky 9369380

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

cc @academo