Fix the parsing of the vagov_info_token cookie

[asg5704]

Description

Currently on VA.gov when the Sign in Service is used to authenticate the vagov_info_token cookie is created as a consumable cookie for the Frontend to get the session expiration. In this Slack thread we want to change this so we can more easily extend our services to others.

**Note, this effort needs to be coordinated launching with vets-api so reach out to a backend engineer before merging in a Pull Request into vets-website

Tasks

• Modify the formatInfoCookie function to parse the string as JSON instead of the custom parsing
• Update unit tests as necessary
• Work with BE team to ensure the PR + their PR is deployed around the same time

[rileyanderson]

New token value example:

{
  "access_token_expiration": "2023-03-17T19:17:31.089Z", 
  "refresh_token_expiration": "2023-03-17T19:29:11.093Z"
}