release-23.1.14-rc: changefeedccl: fix custom key column when used with CDC queries

[blathers-crl]

Backport 1/1 commits from #115163 on behalf of @wenyihu6.

/cc @cockroachdb/release

---

Previously, CDC custom key column caused incorrect behaviour with CDC queries,
leading to a retryable error: No column with name <name> in this row. This was
because we forgot to add columns to colsByName map when generating projection
rows for CDC queries. This caused
DatumNamed
to return a column not found error. This patch addresses the issue by populating
the colsByName map during the addition of columns for CDC queries. Note that
the issue with supporting ALTER CHANGEFEED with CDC queries remains
unresolved.
Fixes: #114196
Release note (bug fix): CDC custom key column now functions with CDC queries
correctly. For example, CREATE CHANGEFEED WITH key_column=..., unordered AS SELECT * FROM table now works correctly instead of retrying forever. Note that
some functionalities with CDC custom keys are not fully supported, see 115267
for more details.

---

Release justification: bug fixes for CDC custom key column when used with CDC queries

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[nicktrav]

EM LGTM ✅

[stevendanna]

I don't have detailed code knowledge here, but the change looks sensible given the commit message description, it includes good test coverage, and the issue seems worth shipping a backport for.