Use create_metadata_json from aind-data-schema

[helen-m-lin]

Is your feature request related to a problem? Please describe.
Metadata file creation logic has been moved to aind-data-schema. Once aind-data-schema is upgraded to >=1.2.0 in this library, we can remove duplicated code in gather_metadata.py.

Describe the solution you'd like

• Use create_metadata_json from aind-data-schema

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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