[feature/frontend] Add options to include Unlisted posts or hide all posts

[tsmethurst]

Description

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This pull request adds a new account setting that determines the visibility of posts that will be included in an account's web view and RSS feeds.

Closes https://github.com/superseriousbusiness/gotosocial/issues/3249 Closes https://github.com/superseriousbusiness/gotosocial/issues/900

Checklist

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

• [x] I/we have read the GoToSocial contribution guidelines.
• [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• [x] I/we have not leveraged AI to create the proposed changes.
• [x] I/we have performed a self-review of added code.
• [x] I/we have written code that is legible and maintainable by others.
• [x] I/we have commented the added code, particularly in hard-to-understand areas.
• [x] I/we have made any necessary changes to documentation.
• [ ] I/we have added tests that cover new code.
• [x] I/we have run tests and they pass locally with the changes.
• [x] I/we have run go fmt ./... and golangci-lint run.