docs: Add workload alerting

[tara-hpe]

Document the experimental feature: Webhooks improvement: see also #9944

Include the use cases: https://hpe-aiatscale.atlassian.net/browse/MD-458

Support workload alerting, different webhook modes, e.g., #9865

Improve the "integrations" section.

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Ticket

Description

Test Plan

Checklist

• Changes have been manually QA'd
• New features have been approved by the corresponding PM
• User-facing API changes have the "User-facing API Change" label
• Release notes have been added as a separate file under docs/release-notes/
  See Release Note for details.
• Licenses have been included for new code which was copied and/or modified from any external code

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[gt2345]

Workload alerting is based on our existing webhook feature, should we update/merge the docs

[tara-hpe]

#9944

yes we'll have to merge #9944 first and then tweak #9938 and remove any duplicates