docs: add ADR for pathway credentials

[Agrendalath]

This adds an ADR defining the initial architecture of the pathway credentials.

Related PRs:

• docs: add ADR for pathway catalog and content split #761
• docs: add ADR for pathway and pathway item boundaries #762
• docs: add ADR for mapping pathway items to fulfillment #763
• docs: add ADR for pathway credentials #764

Private-ref: BB-10965

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[bradenmacdonald]

The decisions make sense, but how will this be implemented? I'm not very familiar with the credentials service / certificates code that exists today, though my impression has always been that it's a bit messy.

Does it already have the primitives you need to issue "pathway" certificates in addition to course certificates?

[Agrendalath]

@kdmccormick, I added a note about the User+Pathway Content relation to a Credential in 3ae128c.

[Agrendalath]

@bradenmacdonald,

The decisions make sense, but how will this be implemented? I'm not very familiar with the credentials service / certificates code that exists today, though my impression has always been that it's a bit messy.

Does it already have the primitives you need to issue "pathway" certificates in addition to course certificates?

Personally, I believe the best approach would be to unify the certificates/credentials across courses and pathways, and move towards their new architecture. However, given that credentials are an important product part of the Pathways MVP and the release timeline is limited, the idea was to quickly replicate the existing course certificate implementation (the one in the openedx-platform, not the credentials service). This will indeed be quite messy, but it will:

1. Speed up the current development process, in terms of reusing the backend and frontend mechanisms.
2. Give us an option to consolidate both certificate types into a new model at once in the future.