Add optional offset to FastaReader

[Taepper]

It should be possible to ingest also partial reads without them needing to contain almost exclusively gap symbols.

[Taepper]

This enables the reading of SAM and other file formats, which do not represent full aligned sequences, but have short aligned reads instead

[Taepper]

We add an integration test folder under testBaseData that contains a test set, which:

• has tests for its preprocessing present in preprocessor.test.cpp
• has tests for its query results in src/silo/test/