Add YAML param files support

[vz10]

Issue #, if available:

Description of changes:
Add support for YAML input files with yaml:// prefix

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[codecov-commenter]

Codecov Report

Merging #5482 into v2 will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##               v2    #5482   +/-   ##
=======================================
  Coverage   94.48%   94.49%           
=======================================
  Files         234      234           
  Lines       17909    17932   +23     
=======================================
+ Hits        16922    16945   +23     
  Misses        987      987           

Impacted Files	Coverage Δ
awscli/paramfile.py	100.00% <100.00%> (ø)

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