Tezlink/Node: import version service

What

• Move the tezlink rpc behind a /tezlink path: http://host:port/chains/mainnet/blocks/head/... is now http://host:port/tezlink/chains/mainnet/blocks/head/...
• add a /version rpc with same spec as tezos version. It's only a mock for now, proper implementation will need to be added (see #7857 ).

Next: /protocols !17392 (merged)

Why

It's a necessary RPC for the demo. We move all rpc to avoid a conflict with the current /version rpc.

We could have:

• used another port, but we don't want to start another rpc server
• change the current /version but that's a big change in the rpc behavior. Also, this doesn't protect us against futur conflicts in rpc path
• have only one rpc but dispatch depending on chain family, but that's confusing UX

How

We import the service from the shell, and implement a dummy version of version.

Manually testing the MR

A new test has been added

dune exec etherlink/tezt/tests/main.exe -- tezlink version