Add `require` parameter for wallet_installPlugins

[rekmarks]

We should add a require parameter for wallet_installPlugins so that domains can request that a specific version of a plugin is installed. The user must install (or already have) a version of the plugin compatible with the semver string value of the require key in the request object. This probably requires proper plugin version management before we can meaningfully implement it.

Similarly, a require:boolean parameter should also be added to rpc-cap for permissions requests: https://github.com/MetaMask/rpc-cap/issues/70

Examples:

// install only
await ethereum.send('wallet_installPlugins', [{
  'http://localhost:8082/package.json': {
    require: '^1.1.0',
  },
}])

// wallet_enable
await ethereum.send('wallet_enable', [{
  'wallet_plugin': {
    'http://localhost:8082/package.json': {
      require: '^1.1.0',
    },
  },
  'eth_accounts': {}
}])

[rekmarks]

Tracked elsewhere.