feat: add support for external sources, from discussion #403

[cseickel]

No description provided.

[codecov-commenter]

Codecov Report

Merging #406 (09e952b) into main (86ec47e) will increase coverage by 0.09%.
The diff coverage is 77.31%.

@@            Coverage Diff             @@
##             main     #406      +/-   ##
==========================================
+ Coverage   53.04%   53.13%   +0.09%     
==========================================
  Files          48       45       -3     
  Lines        5405     5388      -17     
==========================================
- Hits         2867     2863       -4     
+ Misses       2538     2525      -13     

Impacted Files	Coverage Δ
lua/neo-tree/setup/deprecations.lua	42.55% <0.00%> (+1.73%)	⬆️
lua/neo-tree/sources/common/components.lua	60.09% <ø> (ø)
...eo-tree/sources/filesystem/lib/filter_external.lua	7.40% <0.00%> (ø)
lua/neo-tree/setup/init.lua	72.84% <76.92%> (-0.30%)	⬇️
lua/neo-tree/sources/manager.lua	66.03% <85.71%> (+0.22%)	⬆️
lua/neo-tree/ui/highlights.lua	92.73% <90.00%> (-0.25%)	⬇️
lua/neo-tree/command/parser.lua	73.39% <98.00%> (+0.49%)	⬆️
lua/neo-tree/defaults.lua	95.90% <100.00%> (+0.06%)	⬆️
lua/neo-tree/git/status.lua	55.78% <100.00%> (+0.23%)	⬆️
lua/neo-tree/log.lua	42.22% <100.00%> (+1.99%)	⬆️
... and 5 more

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