refactor: move database client to test

[dimbtp]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

Closes #3798

What's changed and what's your intention?

• replace Database client in cli export
• move Database to tests-integration

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[dimbtp]

@MichaelScofield PTAL

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 85.41%. Comparing base (e410192) to head (af71593).
Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3820      +/-   ##
==========================================
- Coverage   85.60%   85.41%   -0.19%     
==========================================
  Files         955      952       -3     
  Lines      163104   162881     -223     
==========================================
- Hits       139625   139127     -498     
- Misses      23479    23754     +275     

[tisonkun]

IIUC we'd letter use https://github.com/GreptimeTeam/greptimedb-ingester-rust.

Although we may not couple this patch with the migration to https://github.com/GreptimeTeam/greptimedb-ingester-rust, we can think of it.

[dimbtp]

@MichaelScofield It is ready for review, please take a look.

[MichaelScofield]

@tisonkun PTAL

[tisonkun]

Thank you! I'll try to delete methods unused in the Database struct.

For further development, I suppose we should make a utility to talk to the server in HTTP API and finally remove all these code. Because we're going to remove the Query variant in GreptimeRequest and most test purpose SQL should be able to run via HTTP API.

And ingestions depend on the Rust ingester library.

[tisonkun]

The next step is replace Database with HTTP API, Rust ingester, or others.