W-17915544 fix: don't lock directory

[mshanemc]

What does this PR do?
whoever originally wrote this (jk, it's me!) locked the parent directory (ex: .sfdx) when creating files there (ex: auth files)

works fine on my machine, might delay things a tiny bit if I'm doing many parallelized things.

cliaas under load from thousands of sandboxes might wait a long time to get to create an auth file, and annoy users or timeout

proper-lockfile https://www.npmjs.com/package/proper-lockfile has the option to not try to resolve the file (by default it does, using realpath option default true)

This change means it puts a lock file in the target folder (ex: sfdx) and if someone else tries to create the same file (ex: auth file) they have to wait for my lock to expire, just like they would for a file that exists.

perf bonus: saves a bit of time for CLI doing fs.existsSync

[realpath option was there to resolve symlinks. None of our auth files are symlinks. If they're in a symlinked dir, it works as expected]

What issues does this PR fix or reference?
@W-17915544@