API not returning useful validation error when FED submitted with undesired datetime format

**Describe the bug in current situation**
When an alteration filing is posted to the API with a FED, the API returns with a 500 internal server error. Note that the corresponding FE ticket is https://app.zenhub.com/workspaces/entity-5bf2f2164b5806bc2bf60531/issues/bcgov/entity/6763

**Impact of this bug**
If the FE fix is deployed there is not much impact. The API should still be fixed to protect itself pro-actively from invalid inputs.

**Steps to Reproduce**
Steps to reproduce the behavior:

1. Post to filings endpoint (e.g. https://legal-api-dev.pathfinder.gov.bc.ca/api/v1/businesses/BC1230084/filings) with payload similar to the following in Postman. Note that the effectiveDate date format is the key thing here. This is what triggers the API 500 error.
```
{
"filing": {
"header": {
"name": "alteration",
"certifiedBy": "",
"date": "2021-03-20",
"folioNumber": "",
"isFutureEffective": true,
"effectiveDate": "2021-03-25T10:02:00.000Z"
},
"business": {},
"alteration": {}
}
}
```
2. API throws 500 error.

**Actual/ observed behavior/ results**


**Expected behavior**
Validation error message should be returned by BE endpoint indicating that the date time format was invalid.