Remove vendored dependencies, upgrade to aws-sdk-go-v2

[gl-johnson]

Desired Outcome

Resolve CVE-2022-0778 and CVE-2022-1292 which are stemming from the vendored version of aws-sdk-go.

Implemented Changes

• Switch repo to go modules
• Migrate from aws-sdk-go (v1.12.14) to aws-sdk-go-v2 (v1.17.5)
• Upgrade Go builder images to 1.19
• Add e2e test

Smoke-tested on MacOS with env variable configuration:

export AWS_REGION=us-east-1
export AWS_ACCESS_KEY_ID=<redacted>
export AWS_SECRET_ACCESS_KEY=<redacted>

summon --provider ./pkg/darwin/summon-s3 \
--yaml 'TEST_CRED: !var glen-johnson.bucket/cred.txt' \
printenv TEST_CRED
hello world!!!!!

Also added an e2e test in CI which does the same as above, but using creds for Cyberark's AWS and a sample s3 secret.
Jenkins: https://jenkins.conjur.net/blue/organizations/jenkins/cyberark--summon-s3/detail/aws-sdk-go-v2/26

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be
merged.

Changelog

• The CHANGELOG has been updated, or
• This PR does not include user-facing changes and doesn't require a
  CHANGELOG update

Test coverage

• This PR includes new unit and integration tests to go with the code
  changes, or
• The changes in this PR do not require tests

Documentation

• Docs (e.g. READMEs) were updated in this PR
• A follow-up issue to update official docs has been filed here: [insert issue ID]
• This PR does not require updating any documentation

Behavior

• This PR changes product behavior and has been reviewed by a PO, or
• These changes are part of a larger initiative that will be reviewed later, or
• No behavior was changed with this PR

Security

• Security architect has reviewed the changes in this PR,
• These changes are part of a larger initiative with a separate security review, or
• There are no security aspects to these changes

[john-odonnell]

LGTM 👍