CodePipeline Codebuild buildspec

[Stretch96]

• Adds the option to specifify a buildspec for the CodePipeline's Codebuild project. By default, it will look for the given filename within the created Codebuild S3 Store, but can optionally be configured to load it from the GitHub repo source instead.
• Creates an S3 bucket where Codebuild buildspecs can be stored. This is where the default buildspec is also stored (dalmatian-default.yml). When custom buildspecs are pushed to the S3 bucket, they can then be specified as the buildspec filename.
• An IAM user is created with a policy that allows S3 read/write permissions, along with an access key that can be used to push custom buildspecs to the bucket.