Introduce GH action for building images with specific version

[kimwnasptd]

Refs #26

This PR:

1. Introduces a releasing directory with helpers for managing the app's release
2. A GH action that uses the releasing/VERSION file to push an image with specific tag, when that file changes

[kimwnasptd]

@StefanoFioravanzo @elikatsis this should be ready for review. We need this in order for the web app to have versions, which I can then include in the KF 1.5 release kubeflow/manifests#2110

This PR:

1. Introduces a releasing/VERSION file, similarly to the one we have in https://github.com/kubeflow/kubeflow/blob/master/releasing/version/VERSION
2. Adds a GH action that will run only when the releasing/VERSION is file. It will build the image with that specific tag and push it

[StefanoFioravanzo]

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kimwnasptd, StefanoFioravanzo

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[kimwnasptd]

It seems that this PR can't be merged as well. @Tomcli any guesses?

@StefanoFioravanzo is a member of KSERVE and I also see in tide's status that the PR is in STATE: MERGE #29 https://kserve-prow-442dbba0442be6c8c50f31ed96b00601-0000.us-south.containers.appdomain.cloud/tide.

I'll move on and manually merge this on, since I needed for the KF release.