[feature] configure bless providers with a role

[ryanking]

Allow configuring bless providers with a role_arn, in addition to a profile.

Support was
previously
added to the provider.

Test Plan

• unit tests

References

• [feature] role auth terraform-provider-bless#33

[codecov-commenter]

Codecov Report

Merging #494 into master will increase coverage by 0.44%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #494      +/-   ##
==========================================
+ Coverage   59.27%   59.72%   +0.44%     
==========================================
  Files          19       19              
  Lines        1994     2001       +7     
==========================================
+ Hits         1182     1195      +13     
+ Misses        654      649       -5     
+ Partials      158      157       -1     

Impacted Files	Coverage Δ
config/v2/config.go	8.60% <ø> (ø)
config/v2/validation.go	78.85% <0.00%> (ø)
config/v2/resolvers.go	50.00% <100.00%> (+0.77%)	⬆️
plan/plan.go	85.94% <100.00%> (+1.96%)	⬆️

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