♻️ Refactor upload image and add max_size

[JMicheli]

As I was reading through the code while preparing to eventually handle the file upload/deletion/bulk management features, I happened on some code for uploading images with a todo marked asking to eventually add configurable max size.

That was easy enough, so I added it as a configuration variable with a default value equal to the prior 20 MB hard-coded limit. I also took the opportunity to refactor the code in the upload module so that it can be more easily reused when other upload types are added.

[codecov]

Codecov Report

Attention: Patch coverage is 25.89286% with 83 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
apps/server/src/utils/upload.rs	30.58%	59 Missing ⚠️
apps/server/src/routers/api/v1/library.rs	0.00%	6 Missing ⚠️
apps/server/src/routers/api/v1/media.rs	0.00%	6 Missing ⚠️
apps/server/src/routers/api/v1/series.rs	0.00%	6 Missing ⚠️
apps/server/src/routers/api/v1/user.rs	0.00%	6 Missing ⚠️

Files with missing lines	Coverage Δ
core/src/config/stump_config.rs	83.85% <100.00%> (+0.25%)	⬆️
apps/server/src/routers/api/v1/library.rs	0.00% <0.00%> (ø)
apps/server/src/routers/api/v1/media.rs	0.00% <0.00%> (ø)
apps/server/src/routers/api/v1/series.rs	0.00% <0.00%> (ø)
apps/server/src/routers/api/v1/user.rs	0.00% <0.00%> (ø)
apps/server/src/utils/upload.rs	26.00% <30.58%> (+26.00%)	⬆️

[aaronleopold]

This looks great! There were a couple of my old TODOs which could be cleaned up I think, but otherwise this looks good to me