Feat: implement rss functionality for profile edit overflow menu

What does this MR do and why?

Closes #416974 (closed), this is a follow up MR for !122971 (comment 1456613603)

/cc @prajnamas @qk44077907 @orozot @fenyuluoshang @icbd

Feat: implement rss functionality for profile edit overflow menu

• Add RSS subscription link to the newly introduced overflow menu.
• Add test cases against the addition.

Screencast for the implementation

CleanShot_2023-07-10_at_14.28.11

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

• Enable FF with Rails Console

Feature.enable(:user_profile_overflow_menu_vue)

1. Go to any profile you want
2. Click on the overflow menu
3. Click Subscribe
4. Observe

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.