Update `SPONSORED_FPC_ADDRESS` throughout the docs to be autogenerated

[critesjosh]

we have these SPONSORED_FPC_ADDRESS=0x1260a43ecf03e985727affbbe3e483e60b836ea821b6305bea1c53398b986047 snippets throughout the docs that frequently go out of date.

potential solution:

use something like #include_code, but that computes and resolves the address, similar to what's done elsewhere in the codebase

  const instance = await getContractInstanceFromInstantiationParams(
    SponsoredFPCContractArtifact,
    {
      salt: new Fr(SPONSORED_FPC_SALT),
    }
  );