Generated java models workflow

[sedovalx]

What does this PR do?:

This PR adds a new workflow to generate, build, and publish java models. The maven publication targets the GitHub packages at the moment, the artifact name is io.devfile:api-model:2.2.0-alpha. I have altered the generate.sh so that it supports both typescript and java now. That potentially can break the typescript-models workflow, though I have run the workflow in my fork and it looked good for all steps before the actual yarn publication (the NPM_TOKEN is missing in my fork).

• Documentation

Updated the README.md to reflect the fact that the generate.sh script can be used for both typescript and java.

• Client Impact

Shouldn't impact existing clients.

How to test changes / Special notes to the reviewer:

I've updated the workflows, so they should be run to verify their correctness.

[openshift-ci]

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[benoitf]

Thx, FYI you need to add SignedOff on the commits

[sedovalx]

Thanks, I will rebase the commits.

Also, can we change

    "attributes": {
      "description": "Map of implementation-dependant free-form YAML attributes.",
      "type": "object",
      "additionalProperties": true
    }

to

    "attributes": {
      "description": "Map of implementation-dependant free-form YAML attributes.",
      "type": "object",
      "additionalProperties": {
        "type": "object"
      }
    }

in the devfile.json for better types generation in java ?

[openshift-ci]

@sedovalx: PR needs rebase.

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