Add SAML integration

[amandahla]

Tested with the change merged on this PR canonical/saml-integrator-operator#37

This PR adds SAML integration by using the SAML Integrator charm library.

What happens after merging it:

• Refactor of database observer.
• Add integration with SAML integrator so the user can enable SAML authentication.
• Add new type SAMLConfiguration.
• Add new observer SAMLObserver.
• Add new configuration public_baseurl.
• Add new container Synapse NGINX as a reverse proxy.
• Add unit and integration tests.

[arturo-seijas]

LGTM

[github-actions]

license-eye has totally checked 69 files.

Valid	Invalid	Ignored	Fixed
38	1	30	0

Click to see the invalid file list

• synapse_rock/attributemaps/u1staging.py

[arturo-seijas]

LGTM

[yanksyoon]

Some small questions, 🎉 LGTM!

[github-actions]

Test coverage for 84f761e

Name                            Stmts   Miss Branch BrPart  Cover   Missing
---------------------------------------------------------------------------
src/actions/__init__.py             3      0      0      0   100%
src/actions/register_user.py       20      0      2      0   100%
src/actions/reset_instance.py      21      3      2      1    83%   54-58
src/charm.py                      110      8     12      1    93%   80-83, 109-110, 170-171
src/charm_state.py                 53      2     10      2    94%   22, 82
src/charm_types.py                 11      0      0      0   100%
src/constants.py                   14      0      0      0   100%
src/database_client.py             53      1     10      3    94%   35, 47->exit, 69->exit
src/database_observer.py           54      4      6      0    93%   70-72, 88
src/exceptions.py                   4      0      0      0   100%
src/observability.py                9      0      0      0   100%
src/pebble.py                      65      4      2      1    93%   87-88, 106-107
src/saml_observer.py               45      1      8      0    98%   64
src/synapse/__init__.py             3      0      0      0   100%
src/synapse/api.py                 83      2     10      1    97%   138-139
src/synapse/workload.py           126      4     18      4    94%   183, 208->211, 227->230, 266, 397-402
src/user.py                        23      0      4      0   100%
---------------------------------------------------------------------------
TOTAL                             697     29     84     13    95%

Static code analysis report

Run started:2023-08-29 13:27:58.597718

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 3041
  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):