release-25.1: sql: don't disable streamer due to scanBufferNode

[blathers-crl]

Backport 1/1 commits from #143151 on behalf of @yuzefovich.

/cc @cockroachdb/release

---

In ed3f640 we disabled the streamer
whenever the plan contains LocalPlanNode processor (which is just
a wrapper around a planNode). This was done to prevent misuse of the
txn API, and we knew at the time that we were disabling the streamer in
more cases than strictly necessary. We just saw a support case where it
was disabled due to scanBufferNode, so this commit includes
scanBufferNode and bufferNode into the allow-list of planNodes that
don't disable the streamer (since these don't interact with internal
executors or the txn in any way).

Also add a few trace messages around this code.

Epic: None
Release note: None

---

Release justification: low-risk improvement.

[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.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
• Backports should not change on-disk formats or node communication protocols.
• Backports should not add new functionality (except as defined
  here).
• Backports must not add, edit, or otherwise modify cluster versions; or add version gates.
• All backports must be reviewed by the owning areas TL. For more information as to how that review should be conducted, please consult the backport
  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.
• Your backport must be accompanied by a post to the appropriate Slack
  channel (#db-backports-point-releases or #db-backports-XX-X-release) for awareness and discussion.

Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[michae2]

Nice!

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @DrewKimball and @mgartner)