feat: FileSystemProvider::readAttributes faked posix support

[nielsbasjes]

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This is the follow up patch after #1066 to add fake posix support in FileSystemProvider::readAttributes.
Important to note is that the values returned in this patch are all fixed and fake.

The main goal of this patch is to have minimal support for the posix attributes because some existing libraries fail if a filesystem does not support this at all. By adding faked support many of these libraries become usable in combination with cloud storage with minimal effort.

I expect that after this some may want to add a more accurate mapping of the attributes.

Fixes #1062 ☕️

[BenWhitehead]

Thanks for opening this PR! I'm reaching out to some teammates to get their input on any gotchas when emulating posix over a gcs bucket.

[nielsbasjes]

Thanks for opening this PR! I'm reaching out to some teammates to get their input on any gotchas when emulating posix over a gcs bucket.

Yes.
In general a GCS bucket cannot do everything a posix filesystem can do.
This PR is not trying to fully emulate posix, only faking the attributes regarding the ownership and permissions. It is really only a view of the attributes.
Having this is enough to get several libraries working in conjunction with a GCS bucket that expect this information in a posix view. Like I ran into here: https://github.com/nielsbasjes/MinimalSftpCloudStorage

So I my view the worst that can happen is that the expected operation fails because the returned fake permission attributes were incorrect (i.e. not allowed to read/write).

[BenWhitehead]

The folks I reached out to didn't have any objections to the approach taken hear.

Thanks for the contribution!