[FEATURE] Define TokenAuthHandlers

[shurwit]

Is your feature request related to a problem? Please describe.
We set up the TokenAuthHandler system in the Core BB (https://github.com/rokwire/core-building-block/blob/d4faf045aed1c83120886a70f879e6c7dd707c4f/driver/web/auth.go#L132), however other BBs should be implementing similar checks.

Describe the solution you'd like
To enable easy and secure validation of tokens, we should expose the TokenAuthHandler struct and related components in the tokenauth package of this library for use throughout the ecosystem.

Describe alternatives you've considered
The alternative is to have each service implement similar checks internally. This would result in inconsistencies, poor maintainability, and potential security flaws.