Display active OT token expiry in token registration page

## Background
OT token "Expiry" is an important piece of information that will determine whether an OT token's "Valid Until" date can be extended further or whether a new token will need to be generated. Although this has been covered in the FAQ, we missed this important detail and expected to see the same token renewed with an extension to the "Valid Until" date. Because of this misunderstanding we renewed the token a bit late and deploying a new OT token took several days (because of unrelated issues in our CI/CD pipelines).

## Request
Include an "Expiry Time" field on the OT token registration page along with some "help" text explaining how a token cannot be extended beyond the expiry date. This will hopefully:
* Make it easy to find a token expiration date (which currently requires using other debug links to figure out)
* help avoid a similar misunderstanding and also avoid a gap in OT participation for other developers in OTs