CLI: Bounty management commands

The CLI currently does not have commands to interact with the Bounty subsystem. This issue outlines that set of commands (based on Bounty module extrinsic):

• Getting information of a bounty
• List of existing bounties (bounties)
• Creating a bounty (create_bounty)
• Canceling a bounty (cancel_bounty)
• Vetoing a bounty (veto_bounty)
• Funding a bounty (fund_bounty)
• Withdrawing funds from the bounty (withdraw_funding)
• Announcing the work entry for a successful bounty (announce_work_entry)
• Withdraw work entry from a bounty (withdraw_work_entry)
• List of work entries (entries)
• Submitting work for a given bounty (submit_work)
• Submitting oracle judgment (submit_oracle_judgment)
• Withdraw work entrant funds (withdraw_work_entrant_funds)

Furthermore, my initial idea for command structure, based on the existing implementation of CLI for different modules, is as follows:

• joystream-cli bounty:bounty
• joystream-cli bounty:bounties
• joystream-cli bounty:createBounty
• ...

This issue is further broken into smaller issues categorizing each into a subset of similar commands.
#3058
#3059
#3060

┆Issue is synchronized with this Asana task by Unito