feat: add PostgreSQL integration

[amandahla]

Applicable spec:

Overview

Maubot requires a database.

Note: This PR is a mashup of code I liked from other charms while working on PostgreSQL integration. I hope you'll find it familiar during your review.

Rationale

Add PostgreSQL integration as required.

Juju Events Changes

database-created
endpoints-changed.

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

No CH available yet

[github-actions]

license-eye has checked 39 files.

Valid	Invalid	Ignored	Fixed
12	1	26	0

Click to see the invalid file list

• lib/charms/data_platform_libs/v0/data_interfaces.py

Use this command to fix any missing license headers

```bash

docker run -it --rm -v $(pwd):/github/workspace apache/skywalking-eyes header fix

</details>

[javierdelapuente]

Nice job. A few comments.

[github-actions]

Test coverage for de0dda3

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py      74      6      8      1    91%   81-82, 109, 113, 122, 144
----------------------------------------------------------
TOTAL             74      6      8      1    91%

Static code analysis report

Run started:2024-09-17 17:17:04.557794

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 272
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[Thanhphan1147]

LGTM, some minor comments