feat: add s3 batch result code constants

[moofish32]

This adds constants and a type for S3 Batch Result Codes similar to what
is available for CodeBuild results

[codecov-commenter]

Codecov Report

Merging #302 into master will decrease coverage by 2.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #302      +/-   ##
==========================================
- Coverage   74.60%   72.46%   -2.15%     
==========================================
  Files          13       18       +5     
  Lines         638      730      +92     
==========================================
+ Hits          476      529      +53     
- Misses        123      136      +13     
- Partials       39       65      +26     

Impacted Files	Coverage Δ
events/epoch_time.go	77.77% <0.00%> (-4.05%)	⬇️
events/cloudwatch_logs.go	60.00% <0.00%> (-3.64%)	⬇️
events/attributevalue.go	80.32% <0.00%> (-2.44%)	⬇️
lambda/panic.go	87.87% <0.00%> (-2.13%)	⬇️
events/duration.go	42.85% <0.00%> (-1.59%)	⬇️
events/code_commit.go	26.08% <0.00%> (-1.50%)	⬇️
events/codebuild.go	44.44% <0.00%> (-1.02%)	⬇️
lambda/handler.go	96.92% <0.00%> (-0.22%)	⬇️
events/lex.go	0.00% <0.00%> (ø)
lambda/rpc.go	55.55% <0.00%> (ø)
... and 8 more

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[bmoffatt]

I think adding the type creates a breaking change. Assignment to a string will require a type cast

ex: https://play.golang.org/p/T5G1eKtbBor

I think leaving the type as string is fine

[bmoffatt]

downside of changing S3BatchJobResult.ResultCode type back to string, is that comparisons against this new type require a cast!

if inputEvent.Results[0].ResultCode == S3BatchJobResultCodeSucceeded {
  // ..
}

->

Invalid operation: inputEvent.Results[0].ResultCode == S3BatchJobResultCodeSucceeded (mismatched types string and S3BatchJobResultCode)

Instead, go back to having S3BatchJobResult being a S3BatchJobResultCode. It is useful for self documentation purposes. But also change the type to be a type alias eg: type S3BatchJobResultCoce = string - this will preserve backwards compatibility.