Add symlink locking for filesystems that do not support hardlinks

[cfxegbert]

In our environment we are using a StorNext file server over Samba on our Mac OSX machines. Mounting over Samba does not allow creating hardlinks. The work done in https://github.com/AcademySoftwareFoundation/rez/pull/903 adds the ability to explicitly use mkdir instead of hardlinks. mkdir may not be an atomic operation on non-local filesystems.

See https://www.mail-archive.com/freebsd-hackers@freebsd.org/msg20456.html

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: cfxegbert / name: Robert Minsk (55052c98f4b687c2fc30cd71ba169a98d48c9301, d45e5d3012903fbae3251c3f86f66700ac347788, b18f8330e7e4aff6cc9bf4d53c1e2366422c56cd)

[JeanChristopheMorinPerso]

@cfxegbert can you fix the DCO thing please? You can follow the instructions at https://github.com/AcademySoftwareFoundation/rez/pull/1708/checks?check_run_id=23579052094.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.27%. Comparing base (1b9c72a) to head (d45e5d3). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1708 +/- ## ======================================= Coverage 58.27% 58.27% ======================================= Files 126 126 Lines 17157 17157 Branches 3504 3504 ======================================= Hits 9998 9998 Misses 6494 6494 Partials 665 665 ```

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[JeanChristopheMorinPerso]

(I rebased the branch to fix a conflict)