Add OpenID Connect integration

[weiiwang01]

Add OpenID Connect integration to the Penpot charm using the oauth charm library.

Since SMTP is required when OpenID is enabled in Penpot, SMTP integration is now a requirement when enabling OAuth.

Integration tests for oauth have been added using oauth_tools from the identity-bundle. However, as there are some issues currently with the oauth_tools, please withhold merging this pull request until the problems have been fixed upstream.

[github-actions]

license-eye has checked 46 files.

Valid	Invalid	Ignored	Fixed
12	1	33	0

Click to see the invalid file list

• tests/integration/prepare.sh

Use this command to fix any missing license headers

```bash

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

</details>

[Thanhphan1147]

LGTM, I only have a few minor comments.

[yanksyoon]

LGTM! Few questions, thank you!

[yanksyoon]

LGTM! Thank you!

[javierdelapuente]

LGTM

[github-actions]

Test coverage for 7eb2df9

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py     238     29     76     17    85%   85-86, 98-100, 114-115, 124-126, 136-138, 147, 154-155, 254, 273, 302, 334, 350, 356, 358, 372, 400, 419, 433, 470, 515
----------------------------------------------------------
TOTAL            238     29     76     17    85%

Static code analysis report

Run started:2024-09-23 06:28:13.602031

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1205
  Total lines skipped (#nosec): 1
  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):