Create a new RNIB-specific output (TBC - HH to continue editing this issue)

[hannahhillen]

Is your feature request related to a problem? Please describe.
It has become apparent that the ONIX 2.1 (EBSCO HOST) output isn't suitable for distribution to RNIB, see #420)
When testing distribution to the platform for Thoth+ package B, RNIB have informed me that the two records submitted for punctum books are missing a synopsis. They have provided the following list for minimum required metadata for books so that they can go live without staff intervention:

-ISBN

-Title

-Author

-Copyright Date

-Copyright holder

-Publish date (the date the publisher has made the title available, if it is in the future)

-Synopsis

-Publisher

-Language

-Country Availability

Additionally, these metadata fields are greatly appreciated as they help RNIB members in search and discovery:

-Related ISBNs

-Subtitle

-Grade level

-Categories/BISAC"

Describe the solution you'd like
Options of altering the ONIX 2.1 output or creating a new RNIB-specific output

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.