Improve currency selection in invoicing (better filtering)

[aimensahnoun]

The current flow of the invoicing template isn't fully optimized.

We want to improve the flow to move Invoice currency as the first selection, which would show us which networks support that currency, then the settlement currency.

Example:

The user selects USDC as the invoice currency; the network dropdown needs to automatically filter which networks support USDC (If celo does not, then celo should not be in the list); then after, based on invoice currency and chain, we show the possible payment settlement currencies.

[MantisClone]

@sstefdev implemented this and it's already in production.