PipelineParameter parses my timestamp strings

I have the following PipelineParameters
```python
train_start_time = PipelineParameter(
name="train_start_time", default_value="2021-01-01T00:00:00"
)
train_end_time = PipelineParameter(
name="train_end_time", default_value="2021-01-31T00:00:00"
)
```
which are passed to my PythonScriptStep as follows:
```python
pipeline_step = PythonScriptStep(
..
arguments=[
"--train_start_time",
train_start_time,
"--train_end_time",
train_end_time,
],
...
)
```
But when I run this in a compute cluster it turns out that the timestamp strings have been parsed, and is passed on to the script in a different format! In `70_driver_log.txt` I see this:
```
[2021-03-23T14:30:23.703839] After variable expansion, calling script [...] with arguments:['--train_start_time', '01/01/2021 00:00:00 +00:00', '--train_end_time', '01/31/2021 00:00:00 +00:00']
```
Iso8601 is the only way to represent time as strings, any other way is abominations! How do I get my pretty strings?

**Edit for extra clarity**:
The problem is that my input string `2021-01-31T00:00:00` gets transformed to `01/31/2021 00:00:00 +00:00` before beeing passed to my script as arguments.

Reproduce the PipelineParameter and PythonScriptStep example with the timestamp values shown, then inspect 70_driver_log.txt for the arguments after variable expansion. Compare the original ISO8601 strings with the transformed values and trace where that conversion occurs. Done means the script receives the original timestamp strings unchanged.

Written by the indexing model from the issue text.