feat: support to configure max database connections for site database users

[tanmoysrt]

Fixes https://github.com/frappe/press/issues/2315 https://github.com/frappe/press/issues/2317 (Check issue for more details)

• [x] Clean up non required fields and functions of old implementation
• [x] Limit database user's max connection. The total allowed connections for each site will be 16 by default. But upon any request, we can configure it from backend
• [x] Frontend Changes
• [x] Allow to set label/title for database user to identify easily (Fixes 2317)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Project coverage is 42.19%. Comparing base (a3face0) to head (0e82652).

Files with missing lines	Patch %	Lines
...s/doctype/site_database_user/site_database_user.py	0.00%	9 Missing :warning:
press/press/doctype/agent_job/agent_job.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2316 +/- ## ========================================== - Coverage 42.19% 42.19% -0.01% ========================================== Files 376 376 Lines 28695 28693 -2 ========================================== - Hits 12109 12107 -2 Misses 16586 16586 ```

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