feat: new runtime API for unique linking

[ntn-x2]

Part of https://github.com/KILTprotocol/ticket/issues/3650, based on top of #784. Last bit of required functionality.

Features

• Since it's not possible to batch multiple runtime API calls, I introduced a batch_ version for our old did runtime API, which allows to do batching instead of firing one request per lookup
• Similarly to that, I introduced a new runtime API (since it's not possible to implement the same API twice for the same runtime), which resolves an account given a name, or a name given an account. This new API also provides a batched version to resolve multiple names or addresses at once. This was one of the requirements we got from Parity to make the solution easier to integrate in the mobile app

How to test

Polkadot Apps support new runtime APIs out of the box. So just compile Peregrine or Spiritnet runtime and spin up a network with Chopsticks. Then:

1. Create a new account-controlled DID. For the Sudo key, use this call 0x401003921cbc0ffe09a865dbf4ae1d0410aa17c656881fe86666da0f97939e3701b674
2. Claim a new dotname. For the Sudo key, use this call 0x400f921cbc0ffe09a865dbf4ae1d0410aa17c656881fe86666da0f97939e3701b674490020746573742e646f74
3. Link the Sudo account to the DID. Use this call 0x400f921cbc0ffe09a865dbf4ae1d0410aa17c656881fe86666da0f97939e3701b6744a01
4. Call the runtime API uniqueLinking.addressForName("test.dot") which should return

{
  Ok: {
    address: {
      AccountId32: 4rDeMGr3Hi4NfxRUp8qVyhvgW3BSUBLneQisGa9ASkhh2sXB
    }
    extra: 4rDeMGr3Hi4NfxRUp8qVyhvgW3BSUBLneQisGa9ASkhh2sXB
  }
}

5. Call the runtime API uniqueLinking.nameForAddress({AccountId32: "4rDeMGr3Hi4NfxRUp8qVyhvgW3BSUBLneQisGa9ASkhh2sXB"}) which should return

{
  Ok: {
    name: test.dot
    extra: 4rDeMGr3Hi4NfxRUp8qVyhvgW3BSUBLneQisGa9ASkhh2sXB
  }
}

[ntn-x2]

@rflechtner perhaps you want to review this PR as well? The new runtime APIs are a result of addressing Parity's requirements. I acknowledge it could be confusing now to have two separate linking features and user-friendly name stuff, as well as two separate runtime API for resolution of those, but I am aiming to discuss about this in next week's tech board.

[ntn-x2]

@Ad96el I'm going to merge this since Parity needs it. Please provide any feedback here and I will address them in a separate PR, thank you!