Diagnostic for FunctionAppLogs does sends datetime using "bad" format

#### Investigative information

- Timestamp: 2022-06-22
- Function App version: 4.6.1.1
- Region: North Europe

#### Repro steps

1. Set up diagnostic settings to send FunctionAppLogs (in my case it is logz.io integration provided by Microsoft)
2. Invoke a function to produce logs
3. check the msg.time property, it looks like that: "06/22/2022 10:24:59"

#### Expected behavior

I expect msg.time to be more precise and use ISO8601 format and not this custom format (which is probably US format):
"time": "2022-06-22T10:20:22.1973786Z"

#### Actual behavior

msg.time property looks like that: "06/22/2022 10:24:59"

#### Known workarounds

Unknown

#### Related information

* Programming language used : net6/C#

Other azure resources with diagnostic settings use the standard format, e.g. Azure Api Management, this is an example:
"time": "2022-06-22T10:20:22.1973786Z",

Start by reproducing the diagnostic-settings flow for FunctionAppLogs and inspect where the msg.time value is serialized. Compare the emitted value with the ISO8601 example in the report; done means the diagnostic payload uses the expected precise ISO8601 timestamp format.

Written by the indexing model from the issue text.