[bugfix] Swagger: add missing filter_action param for v2 filter PUT

[VyrCossont]

Description

This pull request adds Swagger docs for a parameter that should be present on PUT and POST for v2 filters, but was only on the docs for POST.

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.
• I/we have successfully generated code from the Swagger doc (for slurp, in this case)