feat(checker): add fish checker

[ffontaine]

No description provided.

[terriko]

Bumped the branch on this one just to see where the tests are at today.

[ffontaine]

They fails due to OSV on:

=========================== short test summary info ============================
FAILED test/test_source_purl2cpe.py::TestSourceOSV::test_db_contents[1-False] - AssertionError: Missing elements in database: ['pkg:1234n/minicms', 'pkg:13thmonkey/udfclient', 'pkg:23systems/lightbox-plus-for-wordpress', 'pkg:2glux/sexypolling', 'pkg:2pisoftware/cmfive']
assert not ['pkg:1234n/minicms', 'pkg:13thmonkey/udfclient', 'pkg:23systems/lightbox-plus-for-wordpress', 'pkg:2glux/sexypolling', 'pkg:2pisoftware/cmfive']
=========== 1 failed, 295 passed, 2043 skipped in 137.43s (0:02:17) ============