Standardize watcher Download() interface

[djjuhasz]

Refs #867

• Update existing watcher Download() method and interface signatures to take a destination filepath (string) instead of an io.Writer stream
• Add a filewatcher.Download() method
• Create a minio.Download() method and move implementation specific code from serviceImpl.Download() to it
• Update mocks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 67.18750% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 47.23%. Comparing base (e23712e) to head (21095e5).

Files	Patch %	Lines
internal/watcher/minio.go	55.55%	4 Missing and 4 partials :warning:
internal/watcher/filesystem.go	78.78%	4 Missing and 3 partials :warning:
internal/filenotify/filenotify.go	50.00%	2 Missing :warning:
internal/filenotify/poller.go	0.00%	2 Missing :warning:
internal/watcher/watcher.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #868 +/- ## ========================================== + Coverage 45.99% 47.23% +1.23% ========================================== Files 94 94 Lines 5061 5087 +26 ========================================== + Hits 2328 2403 +75 + Misses 2531 2462 -69 - Partials 202 222 +20 ```

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[sevein]

@djjuhasz I think that you're environment is somehow still using an old version of mockgen.

Using bash:

$ source hack/activate/bash 
$ mockgen -version
v0.4.0
$ ls ~/.cache/enduro-sdps/Linux/x86_64/versions/mockgen/
0.4.0

Not sure what's going on. Maybe you're using a version of mockgen installed globally, but that shouldn't happen afaik. You could try this:

$ rm ~/.cache/enduro-sdps/Linux/x86_64/versions/mockgen/*

That would force mockgen to be downloaded again when running: make gen-mock.

[djjuhasz]

@sevein I forgot to do the source hack/activate/bash, so I was generating mocks with mockgen v0.3.0. :( I've just added a commit with the mockgen v0.4.0 output.