feat: add route to return platform known resources

[glinton]

This will add a route to return resources known to the platform. This allows the ui to generate an all-access token in a more uniform, and less brittle, way between cloud and oss.

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (feat: document new route to return known resources openapi#173)

[williamhbaker]

Nice! This will help with influxdata/influx-cli#66 as well.

[glinton]

My biggest concern with this pr is that the list of resources returned aren't filtered in any way. If user doesn't have access to buckets, for example, they will still be responded with buckets as a supported resource. This is only an issue when paired with the use case of using this list to create an all-access token. I don't know how often that particular scenario would likely occur, but reinforces the need to handle the unauthorized errors when trying to grant permission to something the requester doesn't have access to.