Notify community with daily developer build downloads

[davidvonthenen]

What this PR does / why we need it

Since we can't publish a message in the ##tanzu-community-edition slack channel, we have deleted the failed method to publish an RSS feed and instead replaced it with:

• dynamically modifying the README.md with the links for the latest daily build on all supported platforms
• post a thread in a newly created category in the repo's Discussion tab found here: https://github.com/vmware-tanzu/community-edition/discussions/categories/daily-development-builds

Note that on the next successful build, the placeholder text will be updated with each subsequent build's links.

Future TODO: Something that could be cool.... taking that Discussions thread that gets created and maybe using the release tool to provide a commit history between daily builds. Just saying...

Details for the Release Notes (PLEASE PROVIDE)

Notify community with daily developer build downloads

Which issue(s) this PR fixes

NA

Describe testing done for PR

Performed local testing of scripts

Special notes for your reviewer

NA

[stmcginnis]

A small suggestion, but I think it would be fine as a future refinement. This looks good to me.