fix: validate the proposal creation form

[wa0x6e]

Summary

Closes: #517

This PR validates fields on proposal creation.

It adds:

• maxLength validation on the title (256 chars max, limit from offchain)
• maxItems validation on number of choices (500 choices max, limit from offchain)
• maxLength validation on discussion (256 chars max, limit from offchain)
• maxLength validation on body (10k for regular spaces, 40k for turbo, also coming from offchain)

Other changes:

• The form will now always show error on load (so that error show directly when loading a draft, and don't require to dirty fields) (will be extracted to another PR)
• max body length for regular onchain proposals has been bumped to 10k instead of 9600 chars (see fix: show error on Editor composer textarea #520 (comment)). Will revert this if there's some technical constraints preventing that, else will keep this for consistency

How to test

1. Go to the proposal creation page for a turbo space
2. Put some long text in the body textarea
3. It should show an error when the content exceed 40k chars
4. Got to a proposal creation page for a regular space (offchain and onchain), e.g: http://localhost:8080/#/s:pistachiodao.eth/create
5. Put some long text in the body textarea
6. It should show an error when the content exceed 10k chars
7. Same for the title and discussion fields, it should show an error when content exceed 256 chars

TODO

• Waiting for fix: always show voting type selection in Editor #512 merging, as it contains pretty big changes on how Editor and useEditor behave (particularly make it async, by pulling space data). This will avoid duplicate changes on this PR, which also need to pull space data to detected turbo spaces

[Sekhmet]

tACK