start function bound horizontal

[JorgeGtz]

Describe your changes
Update function analyze bound to work with labels

Type of update
Is this a:

• New feature or feature enhancement
• Work in progress

Associated issues
#945

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.

• 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

[codecov]

Codecov Report

Merging #1161 (a6aa676) into release-4.0 (b7a9453) will not change coverage.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           release-4.0     #1161    +/-   ##
==============================================
  Coverage       100.00%   100.00%            
==============================================
  Files              168       170     +2     
  Lines             7351      7576   +225     
==============================================
+ Hits              7351      7576   +225     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
plantcv/plantcv/analyze/color.py	100.00% <ø> (ø)
plantcv/plantcv/analyze/size.py	100.00% <ø> (ø)
plantcv/plantcv/analyze/__init__.py	100.00% <100.00%> (ø)
plantcv/plantcv/analyze/bound_horizontal.py	100.00% <100.00%> (ø)
plantcv/plantcv/analyze/bound_vertical.py	100.00% <100.00%> (ø)