Create documentation for Recurring Donations: BACK-END

[divine-comedian]

Following the project retrospective we should create documentation for the implementation of recurring donations on Base & Optimism for future reference.

Document has already been started here in Notion:
https://www.notion.so/giveth/Technical-Integration-Notes-1733ab28d48c80cd823cd4005efa8dbb?pvs=4

You can see all related superfluid issues/user stories here:
https://github.com/orgs/Giveth/projects/9/views/1?filterQuery=label%3ASuperFluid

Guiding questions

• What Endpoints provided by the back-end?
• Any DevOps related resources it depends on?
• What cronjobs are being used by the feature? What do they do and how do they work?
• SDKs and packages it uses? How does it use them?
• How did you implement each user story/feature?
• Anything tricky or complex or sensitive that future developers should know about?