Feature gql cli print schema

[leszekhanusz]

Adding a new --print-schema argument to gql-cli to allow us to download a schema.

[codecov-commenter]

Codecov Report

Merging #258 (d9fea8b) into master (5df465b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #258   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         1657      1662    +5     
=========================================
+ Hits          1657      1662    +5     

Impacted Files	Coverage Δ
gql/cli.py	100.00% <100.00%> (ø)

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