Re-enable sign-ups, add preOptOutStatus

[Lezek123]

• Re-enable YPP sign-ups in the API
• Add channel's DynamoDB preOptOutStatus field support. This field holds the status/tier that the channel had before being opted out due to Automatic Opt-out of Channels due to Refresh Token Error #337.
• Add HubSpot pre_opt_out_status and opt_out_bug_date fields support
• Add preOptOutStatus field to GET /channels/:joystreamChannelId output
• Assign preOptOutStatus automatically on POST /channels (ie. automatically restore previous tiers of opted-out creators after they sign-up again)

Scripts used for marking opted-out channels in HubSpot and DynamoDB can be found here