add EML generation info to additional metadata?

[atn38]

some items we might need from old EML docs:

• datetime of query from MB
• version of MB queried
• version of MetaEgress used to generate EML
• version of EML R pkg used
• datetime EML was generated
• datetime EML doc was serialized (different from above because you can totally generate the list structure in R way before writing it to .xml file)
• datetime EML was last modified. listing here for completeness, in practice no way in ME you can do this, and you'd look at the file system date modified anyway

[atn38]

metadata about metadata, so to speak

[atn38]

or perhaps in a methodStep