release-25.2: logical: external conn should not require db name

[kev-cao]

Backport 1/1 commits from #155292 on behalf of @kev-cao.

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LDR currently erroneously requires the db name in the external connection with setting up a bidirectional connection. This was determined to be caused by the fact that the privilege lookup on the source cluster was using unqualified table names during the reverse stream setup. This commit fixes the issue by using fully qualified table names.

Fixes: #152395

Release note: LDR no longer requires the database name to be specified in the external connection URI when setting up a bidirectional stream.

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Release justification: Trivial bug fix to unblock broken LDR jobs.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #155735 is compliant with backport policy

Confidence: high
Critical bug criteria met: [Bugs that can cause the DB to return incorrect results or result in suboptimal performance]
Backward compatible: true
Explanation: The pull request fixes a critical bug related to the functioning of the Logical Data Replication (LDR), a product feature of CockroachDB, by addressing an issue where a database name was erroneously required in the external connection URI for bidirectional streams. The analysis determines that this change meets critical bug criteria under 'Bugs that can cause the DB to return incorrect results or result in suboptimal performance' as it deals directly with correcting the setup for bidirectional stream setups which are misconfigured due to improper privilege lookup using unqualified table names. The patch amends the method to utilize fully qualified table names, ensuring proper function of this feature. Additionally, the pull request includes a test file modification, specifically 'pkg/crosscluster/logical/logical_replication_job_test.go', which directly relates to the change and ensures the functionality works as expected after the fix. Considering the changes do not involve any backward-incompatible alterations such as removing version gates and there is no need for feature flag gating since it addresses a critical issue directly, the PR is compliant with the backport policy.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is