Add inputs.roleArn for existing lambda role

[huksley]

Allows to specify ARN of existing role instead of creating a new one.

myNextApplication:
  component: "@sls-next/serverless-component@{version_here}"
  inputs:
    roleArn: "arn:aws:iam::123456789012:role/MyCustomLambdaRole"

• Added to README.md
• Added unit test to packages/serverless-components/nextjs-component/tests/custom-inputs.test.ts

[codecov]

Codecov Report

Merging #827 (427a5a8) into master (178de25) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #827      +/-   ##
==========================================
+ Coverage   80.65%   80.68%   +0.02%     
==========================================
  Files          57       57              
  Lines        1933     1936       +3     
  Branches      431      434       +3     
==========================================
+ Hits         1559     1562       +3     
  Misses        314      314              
  Partials       60       60              

Impacted Files	Coverage Δ
...ges/serverless-components/aws-lambda/serverless.js	73.84% <100.00%> (+0.40%)	⬆️
...rless-components/nextjs-component/src/component.ts	90.78% <100.00%> (+0.12%)	⬆️

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[dphang]

LGTM! Just ran e2e test to check regressions: https://github.com/serverless-nextjs/serverless-next.js/actions/runs/395679068, can merge after

[Arditc]

@dbhagen Just one question regarding this, why aren't we following the same approach of the lambda name?, for constancy and giving the lambda the correct roles:

  roleArn:
      defaultLambda: arn
      apiLambda: arn

The reason I say this is because I wouldn't want to give the defaultLambda access to the database.

I've raised an issue here: #836

[huksley]

Yes, this can be improved if needed @Arditc. I.e use one role if specified directly or use specific roles per lambda if specified as a map as per syntax you show in example.