feat(plugin-bigtable): add Google Cloud Bigtable driver

[i87ce]

Why

TablePro could not open Google Cloud Bigtable.

Change

• A registry plugin, Bigtable Driver, over the Bigtable REST API, with a service account key or Application Default Credentials. Instances are in the database switcher.
• Rows show _key first and one column per family:qualifier. Binary keys and values round-trip as b64: text.
• Filters on _key read row ranges; the rest become row filters that honor case sensitivity. Request-line reads stop at the row limit.
• A new row is an INSERT that refuses a key already in use. Edits are one mutateRow per row, and a row's key cannot change.
• Bigtable and Firebase share one Google REST transport in TableProGoogleCloud, and both split editor scripts as JSON.

Verified

TableProBigtableCoreTests and GoogleRESTRequesterTests. Bigtable added to SQLDDLFallbackPolicyTests, QueryClassifierNonSqlTests and DataChangeManagerImmutableColumnTests. No live-instance run after the rewrite.

Not in this PR

• GoogleSQL: the REST ExecuteQuery answers in encoded protobuf.
• Reverse scans: the REST API answers 501.
• The docs page: docs(databases): add the Bigtable page docs#20, which still describes a new row as PUT.