Add Better Error Message for invalid JSON

If a user tries to make a POST request with JSON, catch the error and return INVALID JSON. More descriptive error.

Currently you get the generic response, and have to check the logs:

{
  "message": "System Error",
  "incidentIdentifier": "-1457776659434189887",
  "details": {}
}

to which if you go to the error in the logs it is immaculate and I immediately knew the issue.

com.fasterxml.jackson.core.JsonParseException: Unexpected character ('}' (code 125)): was expecting double-quote to start field name

Suggest user test JSON payload in VSCode to verify integrity

I.e.

curl -X 'POST' \
  't7hostnamel:tomcatport/swt-data/auth/keys' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "user-id": "myuserid",
  "key-name": "test"
}'

{
  "user-id": "myuserid",
  "key-name": "test"
},

Start at the POST endpoint shown in the issue, /swt-data/auth/keys, and trace how the Jackson JsonParseException becomes the generic System Error response. Reproduce the malformed JSON request, then verify that invalid JSON returns a descriptive INVALID JSON response instead of only the incident identifier and empty details.