add s3 dirctory option

[sadayuki-matsuno]

What did you implement:

I want to put to s3 with a specific directory name.

How did you implement it:

Add S3 directory option -aws-s3-dir=/path/to/results's/parent

How can we verify it:

$ vuls report -to-s3 -format-json -aws-region=ap-northeast-1 -aws-s3-bucket=vuls -aws-s3-dir=something/something -aws-profile=vuls

Todos:

You don't have to satisfy all of the following.

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

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