feat: raw metadata chain config + rename chain

[harrysolovay]

Resolves #621
Resolves #861
Resolves #927

1. exposes API under a chain-specific name instead of chain. This helps us forgo the excessive aliasing.

Before:

import { chain as rococo } from "@capi/rococo-dev-xcm"
import { chain as statemine } from "@capi/rococo-dev-xcm/statemine"
import { chain as trappist } from "@capi/rococo-dev-xcm/trappist"

After:

import { rococoDevXcm } from "@capi/rococo-dev-xcm"
import { statemine } from "@capi/rococo-dev-xcm/statemine"
import { trappist } from "@capi/rococo-dev-xcm/trappist"

2. one can use the codegen with raw metadata.

// ...

export const config: Config = {
  server: "https://capi.dev/",
  chains: {
    polkadotFromMetadata: {
      metadata: await Deno.readFile("metadata"),
    },
  },
}

... then...

import { PolkadotRune } from "@capi/polkadot-from-metadata"

const chain = PolkadotRune.from(connect)

In this case, no chain instance is exposed, as one needs to construct it themselves.