Remove ubi8 workflows, add job to build udi9

[dkwon17]

Part of eclipse-che/che#23034

This PR

• updates the README
• updates the contributing guide
• removes the ubi8 and udi8 build jobs
• adds the udi9 build job

Currently we have:

https://quay.io/repository/devfile/base-developer-image:ubi9-latest

https://quay.io/repository/devfile/base-developer-image:ubi8-latest     ------
                                                                              |-- same image
https://quay.io/repository/devfile/base-developer-image:latest     -----------

After this PR, the ubi9-latest and latest tags will refer to the same image for both base-developer-image and universal-developer-image:

https://quay.io/repository/devfile/base-developer-image:ubi8-latest

https://quay.io/repository/devfile/base-developer-image:ubi9-latest     ------
                                                                              |-- same image
https://quay.io/repository/devfile/base-developer-image:latest     -----------

[svor]

LGTM

[svor]

We might need a follow-up issue to update the image specified in the devfile.yaml for several repositories, such as:

• https://github.com/che-incubator/quarkus-api-example/blob/main/devfile.yaml#L9
• https://github.com/devfile/registry/blob/main/stacks/udi/devfile.yaml#L24
• https://github.com/eclipse-che/che-dashboard/blob/main/devfile.yaml#L8
• https://github.com/eclipse-che/che-server/blob/main/devfile.yaml#L6
• .....

[ibuziuk]

Great Job!

[openshift-ci]

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This pull-request has been approved by: dkwon17, ibuziuk, svor

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