fix(Config Schema): Fix Fn::Join delimiter length schema

[glb]

Allows delimiter to be the empty string as documented by AWS.

Closes: #8344

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@7e4871b). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #8349   +/-   ##
=========================================
  Coverage          ?   88.01%           
=========================================
  Files             ?      249           
  Lines             ?     9307           
  Branches          ?        0           
=========================================
  Hits              ?     8192           
  Misses            ?     1115           
  Partials          ?        0           

Impacted Files	Coverage Δ
lib/plugins/aws/provider/awsProvider.js	93.04% <ø> (ø)

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[medikoo]

Thank you @glb !