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)
• [x] No migrations