Add raw_key field to GPGKey struct

[brekelj1]

This pull request adds the raw_key field to GPGKey. This field is exposed by github.com, for example: https://api.github.com/users/brekelj1/gpg_keys

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[brekelj1]

@googlebot I signed it!

[codecov]

Codecov Report

Merging #2043 (d2fdfb3) into master (b9d1524) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2043   +/-   ##
=======================================
  Coverage   97.87%   97.87%           
=======================================
  Files         107      107           
  Lines        6907     6907           
=======================================
  Hits         6760     6760           
  Misses         81       81           
  Partials       66       66           

Impacted Files	Coverage Δ
github/users_gpg_keys.go	100.00% <ø> (ø)

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[gmlewis]

Thank you, @brekelj1 !
LGTM.
Merging.