Support Course Cert Signatory records in Credentials IDA

[hurtstotouchfire]

• Add support to Credentials for CourseCertificate signatures #1764
• Migrate signature assets from MongoDB GridFS to the Credentials IDA #1765
• Update existing LMS web-certificate code in place to fetch assets from the Credentials IDA #1766

[hurtstotouchfire]

FYI @cdeery

[hurtstotouchfire]

@e0d Do we have a timeline for this? We may need a wiki page.

[deborahgu]

it's my belief that this epic and its associated tickets are no longer happening, is that correct? That is to say, the credentials IDA is not the host of the LMS web certificates, and it is not going to become that host, and it should not be considered a blocker to any future deprecation of the old mongo store that has not been completed.

Could interested parties tell me if I am mistaken about that anyway? Otherwise I will close this epic and the associated tickets.

cc: @justinhynes @GlugovGrGlib