refactor: allow assume role with optional externalId

[pedrokiefer]

Refactor route53 to allow assuming a role, either with the default chain, or using a given key pair.

[CLAassistant]

All committers have signed the CLA.

[pedrokiefer]

@remerle fixed the broken test.

[codecov]

Codecov Report

Base: 92.30% // Head: 91.90% // Decreases project coverage by -0.39% ⚠️

Coverage data is based on head (205fa07) compared to base (f9ee92c).
Patch coverage: 46.66% of modified lines in pull request are covered.

❗ Current head 205fa07 differs from pull request most recent head f6c1ca0. Consider uploading reports for the commit f6c1ca0 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1123      +/-   ##
==========================================
- Coverage   92.30%   91.90%   -0.40%     
==========================================
  Files         173      173              
  Lines        7328     6968     -360     
  Branches      204      176      -28     
==========================================
- Hits         6764     6404     -360     
  Misses        564      564              

Impacted Files	Coverage Δ
...nyldns/route53/backend/Route53ProviderConfig.scala	0.00% <ø> (ø)
.../vinyldns/route53/backend/Route53Credentials.scala	38.09% <38.09%> (ø)
...cala/vinyldns/route53/backend/Route53Backend.scala	82.10% <66.66%> (-1.77%)	⬇️
.../vinyldns/api/domain/record/RecordSetService.scala	90.72% <0.00%> (-2.02%)	⬇️
...nyldns/api/domain/batch/BatchChangeConverter.scala	98.30% <0.00%> (-1.70%)	⬇️
...yldns/api/domain/record/RecordSetValidations.scala	95.57% <0.00%> (-1.55%)	⬇️
...ldns/api/domain/membership/MembershipService.scala	94.77% <0.00%> (-1.53%)	⬇️
...main/scala/vinyldns/api/route/JsonValidation.scala	84.61% <0.00%> (-1.10%)	⬇️
modules/portal/app/controllers/VinylDNS.scala	85.64% <0.00%> (-0.86%)	⬇️
...inyldns/mysql/repository/MySqlZoneRepository.scala	96.42% <0.00%> (-0.41%)	⬇️
... and 41 more

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[Aravindh-Raju]

Tested out locally. Looks good to me!

[pedrokiefer]

I'll close this in favor of #1300, which has signed commits.