Initialize Che Devfile Registry

[sleshchenko]

What does this PR do?

Initialize Che Devfile Registry. Changes are divided into separate commits to make review easier:

1. Add Che 7 Preview Devfile based on the corresponding stack.
   Note that devfile in repository contains extra fields (description, displayName, icon) which are copied to index.json and dropped out from devfile on phase of build.
2. Add an ability to build image for Che Devfile Registry.
3. Set up CentOS CI. It contains build script and job will be created after merging this PR.
4. Add template for deploying Che Devfile Registry to OpenShift.
5. Add helm chart for deploying Che Devfile Registry on Kubernetes.

What issues does this PR fix or reference?

eclipse-che/che#13353
This is only first PR for setting up Che Devfile Registry and the following changes will be set soon:

• set up circleci to perform bash checks;
• add more Devfiles that are based on Che 7 Stacks;
• make API respond with JSON instead of YAML(should be investigated if needed);

Further improvements:

• add JSON Schema check for devfiles in a repository on docker image phase.

How to test this PR

Until cico job is not set, the following image may be used for testing sleshchenko/che-devfile-registry:initial

[sleshchenko]

@slemeur @l0rd you may be also interested in having a look it