meeting proposal: allow to create a public link so that random external people can participate in the date finding process

Is your feature request related to a problem? Please describe.

When I invite other people to find a joint date I often don't know how many people from the other organization will participate. Therefore it is more or less impossible to invite them in advance one-by-one by adding them to the "meeting proposal" explicitly with their email address.

Additionally a automatically generated mail might be confusing for some recipients. I might prefer to send them the link in a personal mail adding some context what the meeting is for and what I expect from them.

Describe the solution you'd like

The user should be able to create a public link for a "meeting proposal", this link can than be send to external people. Once they open the link they should have a option to enter their name and than participate in the process of finding a meeting date. Similar how public polls work.

Describe alternatives you've considered

For the generic mail part I could of course send a personal mail mentioning that they should have received a mail from Nextcloud and what the mail is about. But this is not really convenient, neither for the sender nor for the recipient.

For the other problem, that I don't know all the external people who should join the meeting and their email address because I have just one contact person at the other organization is something I can't solve without a generic public link as described above.

Additional context

No response

Start by reviewing the existing meeting proposal flow and the public poll behavior referenced in the issue. Define how a public link is created and accessed, how external participants enter their names, and how their participation appears in date finding; done means the link supports the complete process without individual invitations.