add Runtime Theming Helm Wiring

[MUFFANUJ]

Reference Issues or PRs

Refs: nebari-dev/nebi#360, nebari-dev/nebi#363

What does this implement/fix?

This PR moves the chart-side runtime theming changes discussed in nebari-dev/nebi#363 into this repository by adding theme values, generating /app/public/config.json from a ConfigMap, and wiring the deployment with NEBI_THEME_CONFIG_PATH plus the required mount and volume.

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

Documentation

None

Access-centered content checklist

Text styling

• The content is written with plain language (where relevant).
• If there are headers, they use the proper header tags (with only one level-one header: H1 or # in markdown).
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• This content adheres to the Nebari style guides.

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Any other comments?

None