Add a placeholder ./local dir

[oalders]

This exists so that this mapping doesn't prevent "docker compose up"
from running:

web-server:
volumes:
- '/app/local'

The purpose of this is to prevent an existing ./local from being mapped
into the container, since there could well be a mismatch between the
locally installed perl used for ./local and the perl which is available
in the container.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.56%. Comparing base (c397d8f) to head (5754676).
Report is 2 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #3334 +/- ## ========================================== + Coverage 73.48% 73.56% +0.08%  ========================================== Files 68 68 Lines 2387 2387 Branches 335 335 ========================================== + Hits 1754 1756 +2  + Misses 507 506 -1  + Partials 126 125 -1 

see 1 file with indirect coverage changes

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