[FEATURE REQUEST] follow_symlinks for file.symlink

[nicholasmhughes]

Is your feature request related to a problem? Please describe.
file.symlink always follows symlinks as it uses os.path.exists() here. This causes performance issues on remote sites when we create symlinks of NFS directories.

Describe the solution you'd like
os.path.lexists() will not follow links during existence checks. Using that function is probably the easiest way to accommodate the requirement.

Describe alternatives you've considered
N/A

Please Note
If this feature request would be considered a substantial change or addition, this should go through a SEP process here https://github.com/saltstack/salt-enhancement-proposals, instead of a feature request.