fix: filter pipeline config files

[anbraten]

closes #271

Done

• filter pipeline config folders for .yml and .yaml files
• improve fetchConfig tests
• update remote mock and correct wrong folder name mock => mocks to match package name
• fix: return correct filename for fallback
• improve config loading by checking if folder or not before sending api call

[6543]

@anbraten

--- FAIL: TestFetch (0.02s)
    --- FAIL: TestFetch/Not_found_and_disabled_fallback (0.00s)
        configFetcher_test.go:164: error fetching config File not found
[0xc00028b140 0xc00028b3e0]
FAIL