feat: administration functions

[killme2008]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Try to implement some administration functions:

• database() to get the current database.
• timezone() to get the current session timezone.
• Added FunctionState for SQL functions to access table or meta service.
• Preparation code for implementing some management functions such as procedure_state(pid) and migrate_region(region, from, to, timeout) etc. I'll implement them in the following PR.

Depends on GreptimeTeam/greptime-proto#137

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.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Attention: 274 lines in your changes are missing coverage. Please review.

Comparison is base (0a9361a) 85.63% compared to head (dc46bab) 85.06%.
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3236      +/-   ##
==========================================
- Coverage   85.63%   85.06%   -0.58%     
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  Files         859      871      +12     
  Lines      140515   141479     +964     
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+ Hits       120333   120344      +11     
- Misses      20182    21135     +953     

[WenyXu]

BTW, I'm not sure whether we should put truncate in the DDL procedure. Maybe we can refactor it in the future PRs. See also: #2968