redirect the subgraph url (for 3rd party clients) on our DNS, so that they are not impacted when we change provider

[levalleux-ludo]

At the moment, the subgraph URL is set in core-sdk configuration, and used as is by all clients.
For instance:

core-components/packages/common/src/configs.ts

Line 168 in 591fc68

"https://api.thegraph.com/subgraphs/name/bosonprotocol/polygon",

Problem is that we need to change the subgraph URL as TheGraph hosted service is getting deprecated soon.
That means every client will have to upgrade their configuration to keep alive.
The idea is to replace this url wirh a constant value (using our DNS, like https://subgraph-polygon-wc.bosonprotocol.io) that always redirect to our subgraph, whatever provider is used behind.

Different subdomain could be used for the different (2rd party) clients we have, so that a discrimination would be possible:

• boson-dcl: https://subgraph-polygon-dcl.bosonprotocol.io, https://subgraph-ethereum-dcl.bosonprotocol.io
• woocommerce: https://subgraph-polygon-wc.bosonprotocol.io, https://subgraph-ethereum-wc.bosonprotocol.io
• a default subgraph (cheap / rate limited) to allow any other 3rd party clients to start easily until they deploy their own subgraph: https://subgraph-polygon.bosonprotocol.io, https://subgraph-ethereum.bosonprotocol.io

Note: the dApp and widgets may not need such an abstraction as we have full control over them: when we change the subgraph, we can upgrade them. IMHO, there is no need to define constant URLs.