Add the ability to download plugins and protoc from specified URLs

[ascopes]

This feature adds the ability to specify specific URLs (file://, http://, https://, ftp://, etc) to reference or download specific binaries for both protoc itself and any binary-based plugins.

This is not usually recommended, and is less secure than the other mechanisms, but is being added to allow the use of plugins that may only be distributed on sources such as GitHub, or on remote servers. It also allows users to reference a specific binary locally without adding it to the system path first, should this be needed.

[codecov]

Codecov Report

Attention: 45 lines in your changes are missing coverage. Please review.

Comparison is base (66bbf0d) 87.74% compared to head (846f60b) 84.13%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #97      +/-   ##
==========================================
- Coverage   87.74%   84.13%   -3.60%     
==========================================
  Files          22       23       +1     
  Lines         644      737      +93     
  Branches       51       53       +2     
==========================================
+ Hits          565      620      +55     
- Misses         57       92      +35     
- Partials       22       25       +3     

Files	Coverage Δ
...tobufmavenplugin/dependency/JvmPluginResolver.java	87.04% <ø> (ø)
...bufmavenplugin/dependency/ResolutionException.java	100.00% <ø> (ø)
...tobufmavenplugin/generate/SourceCodeGenerator.java	98.44% <100.00%> (-0.04%)	⬇️
...tobufmavenplugin/source/ProtoArchiveExtractor.java	97.15% <100.00%> (ø)
...opes/protobufmavenplugin/AbstractGenerateMojo.java	62.50% <87.50%> (+2.86%)	⬆️
...ufmavenplugin/dependency/BinaryPluginResolver.java	85.37% <84.62%> (+3.55%)	⬆️
...s/protobufmavenplugin/generate/TemporarySpace.java	85.72% <33.34%> (-14.28%)	⬇️
...protobufmavenplugin/dependency/ProtocResolver.java	76.93% <69.24%> (-0.85%)	⬇️
...obufmavenplugin/dependency/UrlResourceFetcher.java	53.85% <53.85%> (ø)