Add metadata to outputs

[HaleySchuhl]

Describe your changes
Currently, there is very little metadata in the output file (single-value-traits or multi-value-traits).

Provide metadata to get stored alongside any pcv data:

PlantCV version
Date and time in which the workflow was run
Size of the image (in pixels)

Type of update
Is this a:

• New feature or feature enhancement
• Work in progress

Associated issues

• closes Add image metadata to output file #1592

Additional context
Add any other context about the problem here.

For the reviewer
See this page for instructions on how to review the pull request.

• Wrap all metadata in list within add_metadata method and test functionality in parallel
• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

Here's the code health analysis summary for commits 0d60cc6..9169662. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	✅ Success		View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	100%	100%
Line Coverage	100%	100%
New Branch Coverage	100%	100%
New Composite Coverage	100%	100%
New Line Coverage	100%, ✅ Above Threshold	100%, ✅ Above Threshold

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