Support default non-release version in build-controller-release.sh

[vijtrip2]

Description of changes:

• With the latest addition of presubmit 'release-test' job, service teams are required to execute 'build-controller-release.sh ' script for a successful PR build. 'build-controller-release.sh' script takes VERSION as required parameter.
• Sagemaker team provided the feedback on how they do not want to worry about controller versions until they are doing an actual release. which is fair.
• So this code change, introduces a default version 'v0.0.0-non-release-version' which allows for successful release-test for service teams without worrying about what VERSION to use until actual release.
• This code change also adds the validation for the VERSION parameter.

Why not use something like git describe --tags --always --dirty to generate version ?

• The git command works in most cases if the repository already has a legit semver tag. If that is not the case then we need to add additional handling to create an actual semver tag.
• Instead of dealing with all the edge cases with above command, having a static non-release version gets the job done. Because it is really just a placeholder value for the release-test execution.

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

[jaypipes]

Sweet, thanks @vijtrip2!

[jaypipes]

/lgtm

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