Issue #8417 : Use the unit test database replacement in Database Lookup

[mattcasters]

What this does

A pipeline unit test database replacement was logged and then discarded. Database Lookup, and every other transform that stores a connection name, still opened the original database.

PipelineMetaModifier called DatabaseMeta.replaceMeta() on the object returned by findDatabase(). That load is either a throwaway copy (project JSON metadata) or the shared metadata object (in-memory provider). Transforms never read that object. They keep the connection name and load it again at runtime, so a lookup configured with source-db still opened source-db.

The in-memory test copy now rewrites relational connection names (RDBMS_CONNECTION) from the original connection to the replacement. The project connection and the pipeline on disk are unchanged. Replacements are applied once and do not chain. A connection name that is a variable is resolved first and then stored as the literal replacement name.

Add Sequence, Get Table Names, JDBC Metadata, and Synchronize after merge stored a relational connection without the RDBMS_CONNECTION marker, so those fields are marked as well.

Fixes #8417.

How to verify

./mvnw -pl plugins/misc/testing -am test -Dtest=PipelineMetaModifierTest -Dsurefire.failIfNoSpecifiedTests=false

The test uses a Generic connection with the SQL Server driver class and an H2 replacement. It checks that the copied Database Lookup resolves to the H2 driver, that the original connection is not modified, that a ${DB} reference becomes the literal replacement, and that a missing replacement still fails without touching the source connection.