[BUG] ServiceBus body containing ExpiresAtUtc field is not parsed properly

### Investigative information
###### Please provide the following:

- Related CRI: 219200398
- Timestamp: 2020-12-22 22:58:33
- Function App name: prod-azureing-governor
- Function name(s) (as appropriate):
- Core Tools version:

### Repro steps
###### Provide the steps required to reproduce the problem:
1. Create a function app with service bus trigger.
2. Send a message to the ServiceBus namespace, with ExpiresAtUtc in the body which contains an invalid format.
3. The function's metadata ExpiresAtUtc field will be overwritten by ServiceBus body ['ExpiresAtUtc'].

### Expected behavior
###### Provide a description of the expected behavior.
The function app should not fail since we should not parse of the ServiceBus message.body

### Actual behavior
###### Provide a description of the actual behavior observed.
ValueError: time data '12/18/2020 20:57:23' does not match format '%Y-%m-%dT%H:%M:%S.%fZ'

### Known workarounds
###### Provide a description of any known workarounds.

### Contents of the requirements.txt file:
###### Provide the requirements.txt file to help us find out module related issues.

### Related information
###### Provide any related information

* Links to source
* Bindings used

cc: @gzuber @vrdmr @anirudhgarg @stefanushinardi

Start with the Service Bus trigger behavior described in the reproduction steps and trace how message bodies are handled alongside function metadata. Reproduce the invalid ExpiresAtUtc format, then verify that the body cannot overwrite the metadata value or cause the reported ValueError.

Written by the indexing model from the issue text.