BB2-3483: Fixed date format

[loganbertram]

JIRA Ticket:
BB2-3483

What Does This PR Do?

Fixes access grant expiration date to use ISO-8601, per FHIR expectations.

What Should Reviewers Watch For?

Check access grant expiration format.

If you're reviewing this PR, please check for these things in particular:

Validation

Get an access token and confirm that the "access_grant_expiration" is in ISO-8601 format.

What Security Implications Does This PR Have?

Please indicate if this PR does any of the following:

• Adds any new software dependencies
• Modifies any security controls
• Adds new transmission or storage of data
• Any other changes that could possibly affect security?

• Yes, one or more of the above security implications apply. This PR must not be merged without the ISSO or team
  security engineer's approval.

Any Migrations?

• Yes, there are migrations
  • The migrations should be run PRIOR to the code being deployed
  • The migrations should be run AFTER the code is deployed
  • There is a more complicated migration plan (downtime,
    etc)
• No migrations

[bwang-icf]

Tested and looks right to me!