Swagger: add Link header to all endpoints that use it for paging

[VyrCossont]

Description

Adds description of the Link header to Swagger docs for 5 endpoints that use it but which didn't already have that header in the response description. Also fixes a typo preventing correct docs generation for 1 of those endpoints.

Allows use of Link paging with Swagger clients. No code changes.

Checklist

• 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 not leveraged AI to create the proposed changes.
• 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.