add backend ee route to hit HM

[dpsutton]

Expose an endpoint in an enterprise route that will hit HM, authenticate with email, token, and possibly version(?) to proxy to the FE.

Needs to cache the response. Not exactly clear on how long but on the magnitude of hours seems right.

Handle:

• 200 response
• 500 response
• expired token
• unrecognized token

Decisions we can make in the future (or now):

• can we send the version the FE expects to HM and it can always speak that version?
• if not, if HM responds with a higher version should MB not return any info? Or return a version that the FE won't speak?