Option to disable checking of API Gateway CloudWatch role setting

[coyoteecd]

What did you implement

Provides a roleManagedExternally setting to enable/disable checking of API Gateway CloudWatch role when using provider.logs to enable API Gateway logs. This avoids creating a custom resource lambda (which requires a number of extra permissions assigned to your cfnRole just to run it). You must ensure the setting is there through other means, otherwise the deployment will fail when trying to enable the logs.

Also documents the logging choices available under the Logs section in the API Gateway events doc page.

See also discussion here.

Closes #6973

How can we verify it

provider:
  logs:
    restApi:
       roleManagedExternally: true

Deploying a serverless.yml with roleManagedExternally: false should not create a custom resource. Deployment should succeed when API Gateway already has a CloudWatch role ARN configured in that region (and fail otherwise, obviously).

Default is false, to avoid making it a breaking change.

Todos

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Is this ready for review?: YES
Is it a breaking change?: NO

[medikoo]

Great thanks @coyoteecd, definitely a worthwhile improvement. Please see my remarks

[codecov-io]

Codecov Report

Merging #7333 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7333      +/-   ##
==========================================
+ Coverage   87.92%   87.97%   +0.04%     
==========================================
  Files         240      240              
  Lines        8897     8929      +32     
==========================================
+ Hits         7823     7855      +32     
  Misses       1074     1074

Impacted Files	Coverage Δ
...mpile/events/lib/ensureApiGatewayCloudWatchRole.js	100% <100%> (ø)	⬆️
...lugins/aws/package/compile/events/httpApi/index.js	88.78% <0%> (+4.16%)	⬆️

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[coyoteecd]

Made updates, ready for review

[medikoo]

Thanks @coyoteecd, looks really good. Just proposed few style improvements, and we should be good to go

[medikoo]

Thank you @coyoteecd !