Support for Linkedin Groups

### Category

Social Media

### Website URL

https://www.linkedin.com/groups/144433/

### Website description

I'd like a feed to be returned for Linkedin Groups, such as this one for example: https://www.linkedin.com/groups/144433/ - in much the same way it does for 'Companies' or 'Jobs'.

### What content should be included?

The title, date and body copy. Much as it does with 'Companies' - these appear to be the same from a user perspective, it's just the path I think.

### Additional description

I'm working with a range of organisations. Some have 'Company' pages on Linked which are well supported thanks to this issue which is now satisfied as far as I'm aware: #13563

Some have 'Group' pages - which look pretty much the same to the end user but which are not currently supported by RSSHub.

### This is not a duplicated rss request

- [x] I have searched [existing issues](https://github.com/DIYgod/RSSHub/issues) and [pull requests](https://github.com/DIYgod/RSSHub/pulls) to ensure this rss proposal has not already been requested

Start by locating RSSHub's existing LinkedIn Companies or Jobs route and compare how it handles the group URL path. Confirm the available group content and route behavior before making changes. Done means a LinkedIn group feed returns the title, date, and body copy described in the issue.

Written by the indexing model from the issue text.