Adapt match_variants to allow VCF files as input

[smlmbrt]

Would be useful to be able to match_variants against a set of VCF files. Would require edits to:

• https://github.com/PGScatalog/pgscatalog_utils/blob/a6de70caf9241e0df7a036d4227411957dd08a4b/pgscatalog_utils/match/read.py#L10
• https://github.com/PGScatalog/pgscatalog_utils/blob/a6de70caf9241e0df7a036d4227411957dd08a4b/pgscatalog_utils/match/read.py#L42