[Usage Collection] Supports field descriptions as meta data

[TinaHeiligers]

Resolves #89685

This PR enables support for field-level descriptions to allow developers to document what each field in their collector represents.

The description is support as plain text and makes no assumptions on the length of the string that is provided.

The description is added to an optional new schema field level _meta object that will enable other meta data to be added at a later stage.

Descriptions are added to the localization collector as an initial implementation example.
Before:

schema: {
  locale: { type: 'keyword' },
  integrities: { DYNAMIC_KEY: { type: 'text' } },
  labelsCount: { type: 'long' },
},

After:

schema: {
  locale: {
    type: 'keyword',
    _meta: {
      description: 'The default locale set on the Kibana system',
    },
  },
  integrities: {
    DYNAMIC_KEY: {
      type: 'text',
      _meta: {
        description:
          'Translation file hash. If the hash is different it indicates that a custom translation file is used',
      },
    },
  },
  labelsCount: {
    type: 'long',
    _meta: {
      description: 'The number of translated labels',
    },
  },
},

Adds descriptions to usage collectors in kibana_usage_collection:

• application Usage
• core
• csp
• kibana
• localization
• management
• ops stats
• ui counters
• ui metric

Checklist

Delete any items that are not applicable to this PR.

• Documentation was added for features that require explanation or tutorials
• 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

[afharo]

I noticed 2 gotchas (probably IDE related). Once those are fixed, it LGTM.

[afharo]

LGTM! Pending on green CI! Thank you for doing this @TinaHeiligers

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 97def09
• Storybooks Preview

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
triggersActionsUi	1.6MB	1.5MB	-23.9KB

Page load bundle

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

id	before	after	diff
triggersActionsUi	104.0KB	104.1KB	+82.0B

Unknown metric groups

async chunk count

id	before	after	diff
triggersActionsUi	41	42	+1

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

[kibanamachine]

💔 Backport failed

❌ 7.x: Commit could not be cherrypicked due to conflicts

To backport manually, check out the target branch and run:
node scripts/backport --pr 92701