[bugfix/docs] Poll api fixups + swagger docs

[tsmethurst]

Description

If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.

If this is a documentation change, please briefly describe what you've changed and why.

This pull request fixes up swagger docs for polls, and also ensures that the voted and own_votes fields of polls are always serialized when a user token is presented, even if the value are false/empty.

Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: [ ] -> [x]

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[NyaaaWhatsUpDoc]

that'll do it 🤦‍♀️

[tsmethurst]

Easy thing to overlook when you've been juggling the PR for over a month tbf :P

[NyaaaWhatsUpDoc]

PR for a month, and the branch + code itself for 2 🥲