Add temporary config key instance-connection-enabled

[RaigorJiang]

Fixes #36379.

Changes proposed in this pull request:

• Add temporary config key instance-connection-enabled, the default value is false
• Data sources will be aggregated only when instance-connection-enabled is true and the database type is instance connection available.
• In CatalogSwitchableDataSource, before set catalog, check the current catalog is different or not

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