Providers support a routers 'all' flag for IPIP-0388

[TorfinnOlsen]

IPIP-0388 intends to create an opt-in way for a client to enumerate supported backends, and make a query using a specific backend.

Routing/v1 in Kubo is expected to enable people to do self-hosting of HTTP content router(see WIP PR)

Specifically the request is to enable cid.contact/routing/v1/providers to support '?routers=all' (as an opt-in).

We will likely leverage this from ipfs.io even if we don't make it publicly available.

[TorfinnOlsen]

We need to ensure we have rate limiting in place to leverage.