feat: support set database of the current session

[yezizp2012]

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What's changed and what's your intention?

Resolve #19770 .

dev=> create database d1;
CREATE_DATABASE
dev=> use d1;
NOTICE:  You are now connected to database "d1" as user "root".
USE
dev=> set database to dev;
NOTICE:  You are now connected to database "dev" as user "root".
SET_VARIABLE
dev=> set search_path to "public";
SET_VARIABLE
dev=> show search_path;
  Name
--------
 public
(1 row)

dev=> set database to dev;
NOTICE:  You are now connected to database "dev" as user "root".
SET_VARIABLE
dev=> show search_path;
      Name
-----------------
 "$user", public
(1 row)

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

Support SET DATABASE TO <database_name> and USE <database_name> . Enable switching databases during an active session.

[github-actions]

Hi, there.

📝 Telemetry Reminder:
If you're implementing this feature, please consider adding telemetry metrics to track its usage. This helps us understand how the feature is being used and improve it further.
You can find the function report_event of telemetry reporting in the following files. Feel free to ask questions if you need any guidance!

• src/frontend/src/telemetry.rs
• src/meta/src/telemetry.rs
• src/stream/src/telemetry.rs
• src/storage/compactor/src/telemetry.rs
  Or calling report_event_common (src/common/telemetry_event/src/lib.rs) as if finding it hard to implement.
  ✨ Thank you for your contribution to RisingWave! ✨

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