make taxonomy processing more robust, set when to rely on EML and when not to

[atn38]

The taxonomic capabilities of metabase and MetaEgress have been untested so far AFAIK. They can be reviewed and revised for robustness in anticipation of BLE LTER needing them. In addition, EML moved away from using taxize for their set_taxonomicCoverage function, instead using taxadb which supports fewer taxonomic providers and notably doesn't support WORRMS.

MetaEgress needs to decide:

• how to support providers not supported by taxadb
• how to support multiple providers per set of supplied taxonomies

Ideas:

• use EDI's taxonomyCleanr
• develop different handling for different scenarios