Add-on store front-end: Add support for RSS

[nvdaes]

General descriptions

Users may want to receive notifications when new add-ons are published.
I suggest to add feeds, so that they can be used on mailing lists or in feed readers.

Additional context

I have a bot created by me using GitHub Actions. Currently it's used just on a spanish mailing list, but previously it was used on Mastodon and on a Feeds subgroups of the international add-ons mailing list.
The bot started to fail and I changed it to use the API instead of diffs in this repo.
@seanbudd or others, if you say that this feature is not planned, I'll try to update the bot so that notifications can be submitted in English to the feeds subgroup.
My bot notifies about add-on descriptions and changelog, and sometimes emails are long, so probably I won't add support for Mastodon due to length limitations.
My bot uses Lodash, but I think that a feed from the front-end, maintained by NV Access, would be more robust.
Anyway, my repo is at

https://github.com/nvdaes/nvdaStoreMastodonBot

[seanbudd]

I think conceptually this is fine, but I don't imagine us scheduling this work. We are discussing open-sourcing some of the add-on datastore server code to allow for community contributions like this.
In theory, consumers such as the bot should be able to identify new add-ons using our existing API, by comparing JSON datasets