feat: adding schema.json file to alpha version

[hamza-m-masood]

Which problem does the PR fix?

closes: #2475

What's in this PR?

The readme-generator fails to generate a schema if any value is left empty. So, I added empty strings to each value that was left empty.
here is how you can generate a schema using the readme-generator command:

❯ readme-generator \
--values "./values.yaml" \
--readme "./README.md" \
--schema "./schema.json"

Checklist

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[hamza-m-masood]

@aabouzaid I'm not sure what to do about the sensible defaults on the podDisruptionBudget. What do you think is the best solution here?

Other than empty strings, here are all the sensible defaults I've made: f437894

[hamza-m-masood]

The unit test called TestExistingSecretConstraintDoesNotDisplayErrorForComponentWithExistingSecret is failing in test/unit/camunda I am unsure how to fix it

[hamza-m-masood]

For the ci:
The schema gen step in the make file should only run for 8.7(alpha) and above.
Maybe a condition needs to be added to only run the schema for versions above 8.6

[aabouzaid]

LGTM, thank you Hamza 🙌