feat(auth): add new jsonweb package

[GeorgeMac]

Closes #14971

This introduces the jsonweb package which contains types for parsing JWTs into a type suitable for use as an influxdb.Authorizer. This opens up the ability to start work on jwt based authentication in the API.

The original issue imagined an authorizer type. However, this has evolved into the form of a token type which happens to implement Authorizer interface. The next piece of work will be to integrate this into https://github.com/influxdata/influxdb/blob/master/http/authentication_middleware.go#L104

Update: I have a draft PR of the next piece of work which based on this one here #15151

These could also be merged if that is more preferrable.

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (if modified Go structs or API)
• Documentation updated or issue created (provide link to issue/pr)
• Signed CLA (if not already signed)