RPCs fetch from metadata and selection form explorer

[AugustoL]

Chainlist provides a service where they allow RPCs to be listed on their DB and serve the user with a ranking and stats of the RPCs available.
Openscan is able to do the same, we can add the RPCs to the metadata repository, so any user can propose the addition of new RPCs.
On the explorer we can allow the user to fetch all the RPCs from metadata, see what each of them is offering in privacy and indexing services, and allow the user to select them manually or automaically.