ingest: Update default config params for strain

[joverlee521]

Current default configs for strain requires it to be a non-empty string with accession as the backup field.

pathogen-repo-guide/ingest/defaults/config.yaml

Lines 65 to 69 in 89b3c5d

	# Standardized strain name regex
	# Currently accepts any characters because we do not have a clear standard for strain names across pathogens
	strain_regex: "^.+$"
	# Back up strain name field to use if "strain" doesn"t match regex above
	strain_backup_fields: ["accession"]

This is a historical artifact from when augur required the strain/name column as a metadata id column. Now that we support arbitrary --metadata-id-column across subcommands since Augur 22.1.0, these default config params seem to do more harm than good (e.g. nextstrain/augur#1556 (comment)).

Possible solutions

1. Remove the default backup field.
2. Remove augur curate transform-strain-name and related config params completely since they aren't doing much here if we remove the default backup field.

[joverlee521]

I slightly lean towards [1] in case NCBI Datasets does start to output the strain field, then we can use strain and isolate-lineage as the backup field.

[genehack]

The default params already allow any value other than the empty string, yeah?

[joverlee521]

The default params already allow any value other than the empty string, yeah?

Ah yeah, we just need to remove the default backup field then. Updated issue.