Support gas price estimation

[christianbrb]

Description

Gas prices are fluctuating a lot at the moment. This leads to situations where opening a channel takes 2 hours. We should support the user in setting a good gas price.

CC @agatsoh

Acceptance criteria

Tasks

• [ ]

[andrevmatos]

most onchain txs are done through the main (aka Metamask) account, and on its prompt, you can set your desired gas price, and the SDK will respect and use it. It would only need to be implemented on the SDK for onchain txs sent by the subkey, e.g. token and udc withdrawals.

[christianbrb]

We should at least inform the user about the option in MetaMask: https://metamask.zendesk.com/hc/en-us/articles/360015488771-How-to-Adjust-Gas-Price-and-Gas-Limit-

... and in the long term think about setting the gas price strategy (https://docs.metamask.io/guide/sending-transactions.html#transaction-parameters), which would make eg. opening the channel even more expensive.

[christianbrb]

Discussion about the gas price strategy within the wizard (maybe helpful): raiden-network/raiden-wizard#195

[christianbrb]

Let's skip this for now. Closing