Optimize SAML integration handling

[weiiwang01]

Optimize the handling of SAML integration by utilizing the new SAML Integrator Charm Library. Instead of directly accessing the relation data, use the new SamlRequires.get_relation_data method to obtain SAML information.

[github-actions[bot]]

Test coverage for c87efc3cf5d7b09c443a5aedee9e147b4f8f7254

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/charm.py        335     31     80     12    90%   186, 194-195, 207, 335->343, 376->381, 580-582, 587-588, 599-601, 606-607, 619-621, 626-627, 639-641, 666-668, 710->exit, 720->exit, 750-756, 782->exit, 796-797, 807->exit, 821
src/database.py      30      1      8      1    95%   56
-------------------------------------------------------------
TOTAL               365     32     88     13    90%

Static code analysis report

Run started:2024-03-22 01:23:07.148596

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 1984
    Total lines skipped (#nosec): 3
    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):