Refactor to allow tezos-client to use binary mode

Context

Clients can use binary mode when calling RPCs thanks to the parameter media_type. This parameter has no effect when using tezos-client.

This merge request allows the binary mode for tezos-client.

The function bin_client/Client_rpc_commands.call now uses the new function cctxt#generic_media_type_call instead of cctxt#generic_json_call. This function checks the accepted media_types set in the config and makes the RPC call accordingly.

The test client_binary_mode is adapted to check the correctness of the answer in addition to testing the call success.

Fix: #1921 (closed)

Manually testing the MR

• Call an rpc in json mode (without parameter should work), for exemple you can run tezos-client rpc get /version
• Call the same rpc in binary mode: tezos-client --media_type binary rpc get /version. A binary answer must be displayed
• You can use tezos-coded to decode the binary to check the result.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR