Add Metamask extension for ETH client packages

[pablomendezroyo]

In the app.dappnode.io there is a small pop-up with the Metamask icon suggesting you connect your wallet.

This feature would be really interesting for DAppNode users to connect their wallet to their ETH client dappnode packages (geth, erigon, etc), maybe even with the form fulfilled in Metamask for the "custom RPC endpoint".

Consider:

• [ ] Where to place this feature in the package view
• [ ] Any other wallet extension apart from Metamask
• [ ] Add form/instructions/external link to docs to create a custom RPC with dappnode