use aws-sdk v3

[jsvd]

very naive approach to using aws-sdk v3. needs a lot of require cleanup

Introduce aws-sdk v3, by including the service-specific gems + aws-sdk-core v3, instead of adding the top level ask-sdk gem that would bring on > 300 dependencies.

This PR also removes the calls to eager loading as in aws-sdk v3 it's no longer necessary since we're loading the gems we need explicitly.

[jsvd]

@robbavey I assigned you as a reviewer for this PR. It targets the bootstrap_work branch which is a refresh of your #1 + #3. In the bootstrap_work branch I tried have each commit be a logical change.
The use_aws_sdk_v3 branch does the remaining work on moving the integration to sdkv3, by mostly tweaking requires.

[christianherweg0807]

Hello @jsvd, I've released a pre-version, for testing purposes.
See: https://rubygems.org/gems/logstash-integration-aws

With this test release, I'll be able to test my own prerelease from logstash-input-s3-sns-sqs.
I´ll overhand the rubygems.org artefakt to you/elastic or delete my gem release.

regards
christian

[robbavey]

These changes LGTM - there are a few changes I'd like to see to the bootstrap work branch before we publish, but we can go through those separately to this PR.