Support line commenting with '#'

Low priority, should be dealt with in bulk when doing another major push on dosdp tools. I have seen (for example in ENVO) that people try to comment out rows in a template for provenance reasons.

Start by locating the DOSDP template parsing entry point and checking how input rows are currently interpreted. Clarify the expected behavior for rows beginning with #, then add coverage for the ENVO-style provenance case and verify existing template processing remains unchanged.

Written by the indexing model from the issue text.