Change validation of files (assets) to align with validation on the server

The underlying trigger for the issue is

- https://github.com/dandi/dandi-schema/issues/284

where assets started to fail validation, preventing publishing of dandisets, only when already on the archive. It boiled down to the fails in validation against `jsonschema` export of pydantic models which is done to guarantee that meditor validation could be done online (thus in JS), and the difference in treating `date-time` format by jsonschema and pydantic (datetime).

Looking at the code, in dandi-archive we do

```python
from dandischema.metadata import aggregate_assets_summary, validate
...
metadata = asset.published_metadata()
validate(metadata, schema_key='PublishedAsset', json_validation=True)
```

while in the dandi-cli we do not use `dandischema..validate` construct and rather

```
try:
asset = self.get_metadata(digest=self._DUMMY_DIGEST)
BareAsset(**asset.model_dump())
except ValidationError as e:
if devel_debug:
raise
return _pydantic_errors_to_validation_results(
e, self.filepath, scope=Scope.FILE
)
```

so in effect only validating against Pydantic (and for a BareAsset).

edit 1: moreover we do not even get to above from NWBAsset.get_validation_errors due to

```python
if schema_version is not None:
errors.extend(
super().get_validation_errors(
schema_version=schema_version, devel_debug=devel_debug
)
)
else:
# make sure that we have some basic metadata fields we require
try:
origin = ValidationOrigin(
name="nwbinspector",
version=str(_get_nwb_inspector_version()),
)

for error in inspect_nwbfile(
...
```

so we solely rely on nwbinspector inspection for NWB file but that one does not care about `dandischema` "directly". So we might want to change that one way or another...

We should harmonize, and I feel that here we should use `dandischema.metadata.validate`. I think it also aligns better with our desire to separate models from intended "validity" assumptions.