Reorganize components user guide into other doc sections

[droumis]

Addresses a small part of #3869 (also see #4251) by reorganizing the Components User Guide, and in the process initializes the Background section.

How To > Components:

[codecov]

Codecov Report

Merging #4267 (0e535ac) into main (ff8037e) will decrease coverage by 12.40%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main    #4267       +/-   ##
===========================================
- Coverage   82.71%   70.31%   -12.41%     
===========================================
  Files         237      237               
  Lines       34283    34285        +2     
===========================================
- Hits        28358    24107     -4251     
- Misses       5925    10178     +4253     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	70.31% <ø> (-3.59%)	⬇️

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

Impacted Files	Coverage Δ
panel/pane/vtk/synchronizable_deserializer.py	0.00% <0.00%> (-97.59%)	⬇️
panel/tests/ui/widgets/test_tabulator.py	9.65% <0.00%> (-89.33%)	⬇️
panel/tests/ui/widgets/test_input.py	11.34% <0.00%> (-88.13%)	⬇️
panel/tests/ui/layout/test_accordion.py	14.72% <0.00%> (-85.28%)	⬇️
panel/tests/ui/widgets/test_sliders.py	15.42% <0.00%> (-84.58%)	⬇️
panel/tests/ui/layout/test_card.py	18.01% <0.00%> (-81.99%)	⬇️
panel/tests/ui/io/test_convert.py	15.51% <0.00%> (-80.18%)	⬇️
panel/tests/io/test_notebook.py	20.83% <0.00%> (-79.17%)	⬇️
panel/pane/vtk/synchronizable_serializer.py	1.11% <0.00%> (-76.56%)	⬇️
panel/tests/ui/test_reactive.py	26.53% <0.00%> (-73.47%)	⬇️
... and 49 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[philippjfr]

Looking great, can you:

• Add Background to the top-level TOC
• Remove doc/user_guide/Components.md (as long as all contents have now been migrated)

[philippjfr]

Thanks for the fixes! Looking good.

[philippjfr]

Did you want to remove Remove doc/user_guide/Components.md?

[droumis]

Did you want to remove Remove doc/user_guide/Components.md?

Yep! just removed it. Should be ready to merge now if those were all the comments

[philippjfr]

Perfect, will just go ahead and merge without waiting on tests since those changes shouldn't affect anything.