Added CORS support for the monitoring server

[mdawar]

• Link to issue, e.g. Resolves #NNN
• Documentation added (if applicable)
• Tests added
• Branch rebased on top of current main (git pull --rebase origin main)
• Changes squashed to a single commit (described here)
• Build is green in Travis CI
• You have certified that the contribution is your original work and that you license the work to the project under the Apache 2 license

Resolves #4422

Changes proposed in this pull request:

• Added Access-Control-Allow-Origin header to allow CORS requests for the monitoring server
• Added a check in the tests for the header when the Content-Type is application/json

[aricart]

LGTM - this will add the header and pacify the origin check

[derekcollison]

LGTM