[feat] Add a filesystem-based backend for artifact storage

[gpascale]

Adds FilesystemArtifactStorage, a local filesystem-backed implementation of AbstractArtifactStorage, and adds it to the registry.

Works very similarly to S3ArtifactStorage, except you would pass a url like file:///path/to/artifacts as the uri.

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[gpascale]

I was interested in this, and saw a few issues (#3144, #3139) mentioning it as well, so I thought I'd see if I could implement it. It seems to be working in my very simple setup, but I haven't done that much testing.

Curious for feedback from maintainers as to whether this looks like the correct approach or not.

[alberttorosyan]

@gpascale the changes look good! I've tested them and found no issues.
Would you mind updating the CHANGELOG.md file to reflect the changes and sign the CLA agreement?
We can proceed with the merge right after that

[alberttorosyan]

@gpascale I've pushed changes in CHANGELOG.md. Please complete the CLA so we can proceed with merge.

[alberttorosyan]

@gpascale closing this PR as the CLA is a mandatory step. Will commit changes on your behalf in #3164

[gpascale]

@alberttorosyan Ah sorry for going dark on this. I was travelling the past few weeks and not checking things. Glad to heard you've gotten the feature in!