DPE-3403 Update TLS test lib and test charm

[paulomach]

Issue

• TLS using deprecated v1 lib
• Test using deprecated tls-certificates-operator

Solution

• use lib v2
• use self-signed-certificates

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (53e5474) 65.49% compared to head (2099a2d) 65.49%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #392 +/- ## ======================================= Coverage 65.49% 65.49% ======================================= Files 17 17 Lines 3092 3092 Branches 407 407 ======================================= Hits 2025 2025 Misses 939 939 Partials 128 128 ```

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