Allow stall owners to flag that they're looking for vollies when they submit or update their stall

[keithamoss]

• Only for the "I'm a stall owner" submission flow
• Add a new section "Looking for volunteers" after the "What's on offer?" section
• Allow them to provide either a "Volunteer sign-up link" or "Volunteer contact email" (or both)
• All fields are optional
• When we show the stall on the public map, show a "This stall needs YOU!" call to action above the 'Stall' info block
• Style can be similar to the "Send us a tip-off" call to action for empty stalls
• Clicking the button sends them to the link provided (if present) or a mailto:[email protected] for the contact email provided
• Log an anonymous event in the background to analytics so we know how many people hit the button

Ref: A reply to us on /r/brisbane during QLD 2024