build: upgrade base image & MongoDB; drop py3.8

[uniqueg]

Description

• Drop support for Python 3.8
• Upgrade Docker base image from Debian 11 "Bullseye" to Debian 12 "Bookworm"
• Add support for MongoDB versions "6.0" and "7.0" in CI
• Drop support for MongoDB version "4.2" from CI

Fixes #224 Fixes #226 Fixes #227

Type of change

Please delete options that are not relevant.

• [x] Build update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have updated the documentation (or documentation does not need to be updated)
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have not reduced the existing code coverage

[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (f6526be) to head (e27aead). Report is 7 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #229 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 20 20 Lines 975 975 ========================================= Hits 975 975 ``` | [Flag](https://app.codecov.io/gh/elixir-cloud-aai/foca/pull/229/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai) | Coverage Δ | | |---|---|---| | [test_unit](https://app.codecov.io/gh/elixir-cloud-aai/foca/pull/229/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai) | `100.00% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#carryforward-flags-in-the-pull-request-comment) to find out more.

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