feat(Config Schema): Accept accountId as policy principal

[blue-urban-sky]

Issue around using

    resourcePolicy:
      - Effect: Allow
        Principal:
          AWS: 
           - 123456789012
           - 987654321098

causing a schema validation warning
I have added #/definitions/awsAccountId and updated awsIamPolicyPrincipal to include it as a possible option

Closes: #9077

[codecov]

Codecov Report

Merging #9082 (ac6ee6a) into master (b81fd05) will decrease coverage by 0.01%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #9082      +/-   ##
==========================================
- Coverage   87.17%   87.15%   -0.02%     
==========================================
  Files         288      289       +1     
  Lines       11068    11077       +9     
==========================================
+ Hits         9648     9654       +6     
- Misses       1420     1423       +3     

Impacted Files	Coverage Δ
lib/configuration/variables/sources/file.js	100.00% <ø> (ø)
lib/plugins/aws/package/compile/functions.js	95.89% <ø> (ø)
lib/plugins/aws/provider.js	95.10% <ø> (ø)
scripts/serverless.js	82.95% <0.00%> (-2.93%)	⬇️
lib/classes/CLI.js	94.57% <100.00%> (ø)
lib/classes/PluginManager.js	97.23% <100.00%> (+<0.01%)	⬆️
lib/cli/handle-error.js	86.36% <100.00%> (-1.14%)	⬇️
lib/plugins/aws/package/compile/events/stream.js	98.14% <100.00%> (+0.03%)	⬆️
lib/plugins/aws/package/lib/mergeIamTemplates.js	100.00% <100.00%> (ø)
lib/utils/tokenize-exception.js	100.00% <100.00%> (ø)
... and 1 more

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[blue-urban-sky]

Modified it to allow mixed types

[pgrzesik]

Looks good 👍 I've just added one small comment and we should be good to go 🚀

[pgrzesik]

looks great, thank you @blue-urban-sky 🙇