allow for addition of SQLite table if `.db` file already exists

[dmx2]

human.db file exists, but with human_5mers - if database exists, just write a new table instead of throwing an error

[dan@foxp3 test]$ pepmatch-match -b -q mhc-ligands-test.fasta -p human.fasta 
Traceback (most recent call last):
  File "/home/dan/virtualenvs/python/bin/pepmatch-match", line 8, in <module>
    sys.exit(run_matcher())
             ^^^^^^^^^^^^^
  File "/home/dan/virtualenvs/python/lib/python3.11/site-packages/pepmatch/shell.py", line 58, in run_matcher
    Matcher(**matcher_args).match()
  File "/home/dan/virtualenvs/python/lib/python3.11/site-packages/pepmatch/matcher.py", line 211, in match
    query_df = self._dataframe_matches(self.best_match_search())
                                       ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dan/virtualenvs/python/lib/python3.11/site-packages/pepmatch/matcher.py", line 683, in best_match_search
    matches = self.exact_match_search()
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dan/virtualenvs/python/lib/python3.11/site-packages/pepmatch/matcher.py", line 274, in exact_match_search
    cursor.execute(sql_query, target_kmers)
sqlite3.OperationalError: no such table: human_9mers