chore: Run CodeBuild CI from Github Actions

[lucasmcdonald3]

Issue #, if available:

Description of changes:

• Delete buildspec.yml
• Create .github/workflows/run-codebuild-ci.yml. This implements the CodeBuild CI workflow from buildspec.yml as a Github actions workflow running CodeBuild steps.

Testing:

Successful run: https://github.com/aws/aws-dynamodb-encryption-java/actions/runs/3849450101

There will still be a CodeBuild required check on the PR that will fail, as buildspec.yml was removed. I would plan to delete this check from the repo once a reviewer has approved the PR; see release steps below.

Release steps:

Once PR is in a state with provisional approval and a failing CodeBuild check:

• Delete CodeBuild required check from repo (should remove check from PR)
• Delete CodeBuild webhook from repo
• Confirm all checks succeed; get approval + merge in

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Check any applicable:

• Were any files moved? Moving files changes their URL, which breaks all hyperlinks to the files.

[ajewellamz]

LGTM