feat: allow initializing regions in background

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

1. Introduce initialize_region_in_background, allowing users to initialize all regions in the background without blocking the startup.
2. Introduce the RegionNotReady status code, and non-create/open requests trying to access the region under creating or opening will return the RegionNotReady instead of RegionNotFound.
3. Introduce the RegionBusy status code, ensuring only one exclusive operation(e.g., open region, close region) will be executed simultaneously.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (9da1f23) 85.82% compared to head (43c3e8e) 85.32%.

❗ Current head 43c3e8e differs from pull request most recent head 0ea06e0. Consider uploading reports for the commit 0ea06e0 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2930      +/-   ##
===========================================
- Coverage    85.82%   85.32%   -0.50%     
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  Files          775      770       -5     
  Lines       124230   124430     +200     
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- Hits        106621   106176     -445     
- Misses       17609    18254     +645     

[WenyXu]

@waynexia The new commits changed a lot; it is better to review them again😇

[WenyXu]

@MichaelScofield @fengjiachun PTAL

[MichaelScofield]

@WenyXu conflicts

[WenyXu]

@MichaelScofield @evenyag PTAL