feat: allow global in helm values to allow openfga as dependency chart

[juusujanar]

Allow global property in values schema to be able to use the chart as dependency chart.

Description

This PR adds a global property to openfga Helm chart values schema file. This allows using the Helm chart as a dependency chart and provide values to it.

References

Fixes #106

Review Checklist

• [X] I have clicked on "allow edits by maintainers".
• [X] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [X] The correct base branch is being used, if not main
• [X] I have added tests to validate that the change in functionality is working as expected

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: juusujanar / name: Janar Juusu (a0aad2658e722a25ee6c15ea0947a5f4072c8dff)
• :white_check_mark: login: jon-whit / name: Jonathan Whitaker (7bb22f773af942a4daf7cc44b82f1954ae42d64a)