Add Fleet & Agent 8.11.0 Release Notes

[kilfoyle]

This adds the 8.11.0 Fleet & Elastic Agent Release Notes:

• Fleet Server contents are from BC9 fragments
• Elastic Agent contents are from the BC9 fragments

NOTE: For Fleet I've added a link to the Kibana Release Notes. I think this makes more sense than duplicating the entries in the Kibana Guide and Fleet & Agent Guide, especially if edits to the entries in this PR aren't synced back with the Kibana release notes. Lately the entries have some differences between the two books and I think that could cause some confusion.

DOCS PREVIEW

Closes: #578

[kpollich]

Deferring to the Kibana release notes is fine with me 🚀

[kilfoyle]

Thanks a lot for the careful review @cmacknz! All of your suggestions have been added via 1e7b9b6.

[kilfoyle]

I'll hold off on merging this since we may need to add a breaking change.

[kilfoyle]

@cmacknz
I added the following in 82e69b7. Do you think it captures the breaking change correctly?

(I'll remove it if the release is postponed.)

---

ADD: I've opened a similar PR for the ECE "Limitations and known issues" page: https://github.com/elastic/cloud/pull/121199

[pierrehilbert]

This one is missing:

- kind: bug-fix
  summary: Prevent multiple attempts to stop an already stopped service.
  description: ""
  component: runtime
  pr:
    - https://github.com/elastic/elastic-agent/pull/3482
  issue: []
  timestamp: 1695920792
  file:
    name: 1695920792-Prevent-multiple-stops-of-services.yaml
    checksum: 8a0b54855b27c98e6af3d60df1c9cb04f935efee

[pierrehilbert]

 - kind: breaking-change
      summary: Enable compression by default for Elasticsearch outputs
      description: 'The default compression level for Elasticsearch outputs is changing from 0 to 1. On typical workloads this is expected to decrease network data volume by 70-80%, while increasing cpu use by 20-25% and ingestion time by 10%. The previous behavior can be restored by adding ''compression_level: 0'' to the output configuration.'
      component: all
      pr:
        - https://github.com/elastic/beats/pull/36681
      issue:
        - https://github.com/elastic/ingest-dev/issues/2458
      timestamp: 1696361138
      file:
        name: 1696361138-es-default-compression.yaml
        checksum: f3bee390b1af6bc5049315e25e5c14d0ff23240e

[pierrehilbert]

- kind: feature
      summary: Add component {id, binary} to monitoring metrics from Elastic-Agent and Beats.
      description: ""
      component: elastic-agent
      pr:
        - https://github.com/elastic/elastic-agent/pull/3626
      issue:
        - https://github.com/elastic/integrations/issues/7977
      timestamp: 1697735373
      file:
        name: 1697735373-Add-component-fields-to-metrics.yaml
        checksum: e78d27aa33269834757dceee23e195ae6ea8ecd5

[kilfoyle]

Thanks @pierrehilbert

• I've added the missing bug fix for Fix double stop components elastic-agent#3482
• Enable compression by default for Elasticsearch outputs beats#36681 is in the "Breaking changes" section: Compression is enabled by default for Elastic Agent Elasticsearch outputs
• I'm confused about Add component.{id, binary} to monitoring metrics elastic-agent#3626 I don't see it in the BC9 fragments so I thought it didn't make it into the release. Should I still add it?

[cmacknz]

The commit for BC9 is https://github.com/elastic/elastic-agent/commits/3c8be7201bbf4e3f91d7b56de9ff285c386a7804 so David is correct that elastic/elastic-agent#3626 did not make 8.11 release.

[kilfoyle]

Thanks to feedback from @mieciu I've updated (and softened) the breaking change description: