use `format_datetime` from thoth.common when available in PyPI

[todo]

osiris/osiris/schema/build.py

Lines 82 to 87 in 3be2e67

	# TODO: use `format_datetime` from thoth.common when available in PyPI
	first_timestamp=start_ts,
	last_timestamp=end_ts,
	ocp_info=ocp,
	**kwargs
	)

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This issue was generated by todo based on a TODO comment in 3be2e67 when #15 was merged. cc @CermakM.