Fix JIRA client spec failing due to time differences

What does this MR do and why?

Jobs such as https://gitlab.com/gitlab-org/gitlab-foss/-/jobs/1686583500 were intermittently failing because the Authorization header would have slightly different JWTs. It turns out the iat and exp fields were off by a second since the test might generate the field before the test made the HTTP request.

We fix this issue by freezing the time whenever we need to make an HTTP request.

Screenshots or screen recordings

Example JWT discrepancy:

Actual

{
  "iss": "gitlab-jira-connect-localhost",
  "iat": 1634490113,
  "exp": 1634490173,
  "qsh": "0947f5bc05f2c4728bc2e3905089951a4aa601772a79268aa983e2ef881b79ff"
}

Expected

{
  "iss": "gitlab-jira-connect-localhost",
  "iat": 1634490114,
  "exp": 1634490174,
  "qsh": "0947f5bc05f2c4728bc2e3905089951a4aa601772a79268aa983e2ef881b79ff"
}

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