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/dashboarddatasetschema.Schema.json

@@ -0,0 +1 @@
+{"schema":{"properties":{"always_filter_main_dttm":{"type":"boolean"},"cache_timeout":{"type":"integer"},"column_formats":{"type":"object"},"column_names":{"items":{"type":"string"},"type":"array"},"column_types":{"items":{"type":"integer"},"type":"array"},"columns":{"items":{"type":"object"},"type":"array"},"currency_code_column":{"type":"string"},"database":{"properties":{"allow_multi_catalog":{"type":"boolean"},"allows_cost_estimate":{"type":"boolean"},"allows_subquery":{"type":"boolean"},"allows_virtual_table_explore":{"type":"boolean"},"backend":{"type":"string"},"disable_data_preview":{"type":"boolean"},"disable_drill_to_detail":{"type":"boolean"},"explore_database_id":{"type":"integer"},"id":{"type":"integer"},"name":{"type":"string"}},"type":"object","title":"Database"},"datasource_name":{"type":"string"},"default_endpoint":{"type":"string"},"edit_url":{"type":"string"},"fetch_values_predicate":{"type":"string"},"filter_select":{"type":"boolean"},"filter_select_enabled":{"type":"boolean"},"granularity_sqla":{"items":{"items":{"type":"string"},"type":"array"},"type":"array"},"health_check_message":{"type":"string"},"id":{"type":"integer"},"is_sqllab_view":{"type":"boolean"},"main_dttm_col":{"type":"string"},"metrics":{"items":{"type":"object"},"type":"array"},"name":{"type":"string"},"normalize_columns":{"type":"boolean"},"offset":{"type":"integer"},"order_by_choices":{"items":{"items":{"type":"string"},"type":"array"},"type":"array"},"owners":{"items":{"type":"object"},"type":"array"},"params":{"type":"string"},"perm":{"type":"string"},"schema":{"type":"string"},"select_star":{"type":"string"},"sql":{"type":"string"},"table_name":{"type":"string"},"template_params":{"type":"string"},"time_grain_sqla":{"items":{"items":{"type":"string"},"type":"array"},"type":"array"},"type":{"type":"string"},"uid":{"type":"string"},"verbose_map":{"additionalProperties":{"type":"string"},"type":"object"}},"type":"object","title":"DashboardDatasetSchema"},"schemaType":"response"}