Make it easier to connect multiple accounts to a single Dapp

[bbondy]

Currently the only way to change the connected account list for a Dapp is to:
i) Disconnect all accounts and request permission again from the site
ii) Lock the wallet after connecting a single account and request permissions again from the site

We should have some easier way in the panel to connect even without the Dapp requesting it.

[Douglashdaniel]

Was addressed in this PR brave/brave-core#11486
Closing as duplicate