Add option to use sourmash to search instead of diamond

[olgabot]

don't convert between hashes <> kmers <> seqs, but instead search for hashes directly

PR checklist

• [x] This comment contains a description of changes (with reason)
• [x] If you've fixed a bug or added code that should be tested, add tests!
• [x] If necessary, also make a PR on the nf-core/predictorthologs branch on the nf-core/test-datasets repo
• [x] Ensure the test suite passes (nextflow run . -profile test,docker).
• [x] Make sure your code lints (nf-core lint .).
• [ ] Documentation in docs is updated
• [x] CHANGELOG.md is updated
• [x] README.md is updated

Learn more about contributing: CONTRIBUTING.md

[pranathivemuri]

seems like tests are getting canceled - https://github.com/czbiohub/nf-predictorthologs/pull/35/checks?check_run_id=600390407#step:5:37

[olgabot]

I am completely unable to test this on my home machine due to a bizarre docker/nextflow issue of directories not being mounted (nextflow google group message).. I have no idea why it's happening. But if all the tests are working here, including test_diff_hash_sourmash then I'm happy to merge!