Proto/Client: remove some duplicated code related to `fee_parameter`

This MR removes duplicated code in the client, namely the handling of Injection.fee_parameter. This requires a modification in lib_clic to allow multiple Clic's arguments to be merged into a single value.

This MR is extracted from !5106 (closed) and is also used by !5168 (closed).

How to test.

There is no visible new feature. The following options of some command in tezos-client should work as before:

• --force-low-fee
• --fee-cap
• --burn-cap
• --minimal-fees
• --minimal-nanotez-per-gas-unit
• --minimal-nanotez-per-byte