Pre-proposal backing

An extension/alternative to https://github.com/Joystream/joystream/issues/2529

The issue with the previously suggested system is that it still has a significant barrier for new users. It does not reduce the price of proposal creation, so in order to sufficiently prevent spam attacks and problematic proposals being submitted repeatedly the price would always need to remain artificially high to the detriment of new users to the platform.

A better alternative may be to allow the creation of pre-proposals. These would be proposals that have a reduced fee, and require community funding in order to become active proposals

An example:

• pre-proposal cost: 1500 JOY
• pre-proposal timer: 3 weeks
• proposal cost: 25000 JOY
• on Pioneer v2 having approved proposals is shown on a users profile, so this is an activity people would want to have in order to build and secure their on-chain reputation

Alice has an idea for launching a cool competition on Joystream, the competition is well written and it is a high quality contribution, however they are new to the platform and do not possess a significant number of tokens. Rather than put the idea on the forum and allow someone else to get the credit of creating a proposal, they create a pre-proposal by paying 1500 JOY (this could either be staked or burned depending on if this idea is implemented). While this does not get listed along with the real proposals it can be separately listed in Pioneer with other pre-proposals.
When the pre-proposal is created, it has a discussion section, but does not have any voting options for the council (yet)
Interested community members have an incentive to bring good propopsals to the council's attention, so after seeing Alice's proposal, 12 people contribute the remaining proposal fee of 25000 JOY.
This then triggers the proposal to turn from a pre-proposal to an active proposal

In an alternative scenarion, the pre-proposal does not get enough attention and 3 weeks pass, after which the pre-proposal fails and the pre-proposal fee is either burned or returned.

No files, tests, or entry points are identified. Start by reviewing issue #2529 and the existing proposal flow, then clarify the pre-proposal lifecycle, funding, expiry, and conversion requirements before implementation; completion criteria are not defined in this issue.