feat: ensure plugins directory exists

[alexbarnsley]

Proposed changes

Make sure the plugin directories exist so the user doesn't have to figure out how to create them (e.g. Windows)

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes

[codecov-io]

Codecov Report

Merging #1195 into v2.4.0 will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           v2.4.0    #1195      +/-   ##
==========================================
+ Coverage   38.72%   38.72%   +<.01%     
==========================================
  Files         222      222              
  Lines        5883     5882       -1     
  Branches     1165     1169       +4     
==========================================
  Hits         2278     2278              
+ Misses       3407     3406       -1     
  Partials      198      198

Impacted Files	Coverage Δ
src/renderer/services/plugin-manager.js	2.42% <0%> (+0.01%)	⬆️
src/renderer/components/Network/NetworkModal.vue	4.22% <0%> (ø)	⬆️

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