Add missing allowed value not mentioned in the docs

[fatbasstard]

Fix a missing Allowed value. Not in the CLoudFOrmations docs, but are in the API docs:

https://docs.aws.amazon.com/dlm/latest/APIReference/API_PolicyDetails.html#dlm-Type-PolicyDetails-ResourceTypes

Along came some spec changes

[codecov]

Codecov Report

Merging #995 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #995   +/-   ##
=======================================
  Coverage   86.83%   86.83%           
=======================================
  Files         133      133           
  Lines        7878     7878           
  Branches     1939     1939           
=======================================
  Hits         6841     6841           
  Misses        639      639           
  Partials      398      398

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