Callback support to set method in social-db

[Tguntenaar]

This is actually a feature request for social-db but has effect on devhub. This ticket is used to track the progress on our board.

Is your feature request related to a problem? Please describe.

A community discussion post works as follows:

1. a users posts to his/her social-db account
2. the discussions account (discussions.${handle}.community.devhub.near) than reposts the users post using the blockheight.

Right now we match content of the latest social-db post before reposting to a discussions.${handle}.community.devhub.near account. This is done in order to wait for the correct blockheight.

Describe the solution you'd like

A better fix would be to introduce a callback support to set method implementation of SocialDB, so calling set we can ask it to call devhub.near contract passing the block height and the keys that were updated (frol.near/post/main)

Describe alternatives you've considered

The alternative is what is implemented now via this PR: https://github.com/NEAR-DevHub/neardevhub-bos/pull/670

Additional context

See these discussions on telegram from more context:

1. https://t.me/c/1822948693/5050/5185
2. https://t.me/NearSocialDev/5882