splitted ltm- and stm-memory roots for FileHandler to avoid tmp-clear…

[Lukas113]

Split long-term-memory disk-cache root from short-term-memory. The reason for this change is because before a differentiation between the two use-cases regarding the root-directory was not possible. Therefore, the default root-dir /tmp caused to remove long-term-memory files at each restart, which is not desired.

• The previous root is now the default for short-term-memory
• Long-term-memory directory now follows the XDG Base Directory Specification.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 63.88889% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 66.93%. Comparing base (d423934) to head (d32d23c).

Files	Patch %	Lines
karabo/util/file_handler.py	63.88%	13 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #564 +/- ## ========================================== + Coverage 66.88% 66.93% +0.04% ========================================== Files 49 49 Lines 4980 4996 +16 ========================================== + Hits 3331 3344 +13 - Misses 1649 1652 +3 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.