docs: cut 6.1.0 versions for user_docs, admin_docs, developer_docs, components

Snapshots all four versioned Docusaurus sections at v6.1.0, cut from
master after the version-cutting tooling (#39837), broken-internal-
links fix (#40102), and user_docs rename (#40171) all landed. With
the rename in place, all four sections now produce parallel-named
files at the docs/ root (no more bare `versioned_docs/` outlier).

Versioning behavior: lastVersion stays at current for every section,
so the canonical URLs (/user-docs/..., /admin-docs/...,
/developer-docs/..., /components/...) continue to render content
from master. The current version is consistently labeled "Next"
with an unreleased banner, and 6.1.0 is a historical pin accessible
only via its explicit version segment.

Component playground: previously disabled: true in versions-config.json,
now enabled and versioned.

Snapshot includes:
- All MDX content for the four sections.
- Auto-gen captured fresh: 74 database pages (engine spec metadata),
  ~1,800 API reference files (openapi.json), 59 component pages
  (Storybook stories).
- Data imports frozen at cut time into snapshot-local _versioned_data/
  dirs:
    user_docs_versioned_docs/version-6.1.0/_versioned_data/src/data/databases.json
      (canonical 80-database diagnostics from master, preserved by the
      generator's input-hash cache)
    admin_docs_versioned_docs/version-6.1.0/_versioned_data/data/countries.json
    admin_docs_versioned_docs/version-6.1.0/_versioned_data/static/feature-flags.json
    developer_docs_versioned_docs/version-6.1.0/_versioned_data/static/data/components.json
- Import paths in deeply-nested files rewritten so they still resolve
  from one directory deeper inside the snapshot.
- developer_docs/extensions/overview.md snapshot has the FIXED
  ./mcp.md form (from #40102), so the SPA-nav 404 isn't baked into
  the 6.1.0 version.

Verified via full yarn build: exit 0, no broken links surfaced by
onBrokenLinks: throw.

docs/developer_docs_versioned_docs/version-6.1.0/api/schemas/slice.Schema.json

@@ -0,0 +1 @@
+{"schema":{"properties":{"cache_timeout":{"description":"Duration (in seconds) of the caching timeout for this chart.","type":"integer"},"certification_details":{"description":"Details of the certification.","type":"string"},"certified_by":{"description":"Person or group that has certified this dashboard.","type":"string"},"changed_on":{"description":"Timestamp of the last modification.","format":"date-time","type":"string"},"changed_on_humanized":{"description":"Timestamp of the last modification in human readable form.","type":"string"},"datasource":{"description":"Datasource identifier.","type":"string"},"description":{"description":"Slice description.","type":"string"},"description_markeddown":{"description":"Sanitized HTML version of the chart description.","type":"string"},"edit_url":{"description":"The URL for editing the slice.","type":"string"},"form_data":{"description":"Form data associated with the slice.","type":"object"},"is_managed_externally":{"description":"If the chart is managed outside externally.","type":"boolean"},"modified":{"description":"Last modification in human readable form.","type":"string"},"owners":{"description":"Owners identifiers.","items":{"type":"integer"},"type":"array"},"query_context":{"description":"The context associated with the query.","type":"object"},"slice_id":{"description":"The slice ID.","type":"integer"},"slice_name":{"description":"The slice name.","type":"string"},"slice_url":{"description":"The slice URL.","type":"string"}},"type":"object","title":"Slice"},"schemaType":"response"}