Remove docs for removed keyring/credstash options

[hmmbob]

Proposed change

Remove docs for removed keyring/credstash options.

The methods of storing secrets in credstash and keyring have been removed. They have been deprecated and a warning has been printed since Home Assistant 2020.12. Support is removed in 2021.3.0

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Remove deprecated credstash + keyring core#47033
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue:

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[frenck]

There are also shown in the aside bar as links, that need to be cleaned up. Additionally, add a redirect to removed integrations for these paths in the _redirects file, so people don't land on a 404 following an old link.

[hmmbob]

Good catch. Did a search for credstash and keyring on my forked repo through the github site but nothing had popped up. Searching for it on the main repo shows them as expected. Found a leftover as well.

I redirected the two pages to the secrets page, as that looked more like what we did with other doc redirects and it is the alternative to the deprecated functionality. Let me know if this is ok, or if it should redirect to removed integration regardless.

[frenck]

Thanks, @hmmbob 👍