BREAKING: Add JSON-RPC handler permission

[Mrtenz]

This adds a new permission endowment:rpc, which Snaps need in order to use the onRpcRequest handler. It takes an object in order to specify if the Snap can receive JSON-RPC requests from other Snaps, Dapps, or both.

{
  initialPermissions: {
    'endowment:rpc': {
      snaps: true,
      dapps: false, // Default value
    }
  }
}

Closes #855.

[Mrtenz]

Pending a release of @metamask/controllers.

[codecov-commenter]

Codecov Report

Merging #905 (3d069ae) into main (421c727) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #905      +/-   ##
==========================================
+ Coverage   92.98%   93.02%   +0.03%     
==========================================
  Files          96       96              
  Lines        9642     9690      +48     
  Branches      905      909       +4     
==========================================
+ Hits         8966     9014      +48     
  Misses        676      676              

Impacted Files	Coverage Δ
packages/snaps-utils/src/caveats.ts	100.00% <100.00%> (ø)
packages/snaps-utils/src/json-rpc.ts	100.00% <100.00%> (ø)
packages/snaps-utils/src/manifest/validation.ts	100.00% <100.00%> (ø)

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