feat: support symlink resolution to one level

[michaelschuett-tomtom]

Changes

This supports symlink files to be uploaded provided it can resolve the link. For the golang API this means the link points directly do regular file. If the symlink points to another symlink it will fail and databricks will act exactly as it does today and ignore the file.

This is largely because I want to write a bazel rule that uses databricks and without this support it's close to impossible as bazel heavily uses symlinks.

Tests

1. Created a symlink and ran databrick bundle deploy and see it's uploaded to the files folder.
2. Create a symlink that points to another symlink and see that no error is thrown.
3. Create symlinks that reference each other and see that no error is thrown.

[michaelschuett-tomtom]

I think the only open question provided this is accepted is if we should ever throw errors around symlinks since this will be a breaking change. Not returning any errors but supporting them would not be a breaking change.

[pietern]

Thanks for posting the PR.

I commented in #1706 (comment) with the rationale for not resolving symlinks. Let's continue the thread there.

[pietern]

In the linked comment I propose using rsync -L to build a symlink-free copy of the tree prior to calling bundle commands.

Adding proper symlink support introduces quite a few difficult corner cases I'd rather not have to deal with.

I'm closing this PR, but we can revisit it if there is more evidence that suggests the benefits outweigh the costs.