Added support to upload assets using DRM playback policy. It includes updates to the configuration UI, asset editing workflow, token generation logic, and player code generation.

Disclaimer:
This PR is blocked until we decide what to do with the DRM preview in contentful, and closes #185.

The app configuration screen now includes a new "Advanced: DRM" section. Users can enable or disable DRM support and provide a DRM Configuration ID, which is stored alongside other installation parameters.
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The asset configuration modal has been updated to include a "DRM Protected" option in the playback policy selector. This option becomes available only when DRM is enabled and a DRM Configuration ID is present; otherwise, it appears disabled with contextual help text. DRM is never selected by default, even when enabled, to avoid accidental use of a paid feature.
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(In the example, the user did not set a DRM Configuration ID)

In the main app view, the app now detects when an asset uses a DRM playback policy. When this occurs, it requests DRM license tokens through a new App Action (getDRMLicenseTokens). The action generates all required tokens (license, playback, thumbnail, and storyboard) and these are passed to the MuxPlayer component through the tokens property. A new lock indicator shows when an asset is DRM-protected. Since assets may include multiple playback IDs, additional logic has been added for prioritizing which ID is displayed and which one is used during playback: the UI prioritizes Public → Signed → DRM, while playback always respects the selected policy.

When the DRM Configuration ID set by the user is not valid, the following message is shown in the UI when trying to activate the DRM protected playback in an asset (the text comes from the response from the API):
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When viewing DRM assets inside Contentful, a warning message explains that DRM cannot be rendered in the preview.
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Finally, the generated player code now includes DRM tokens and assigns them to the player.tokens property so that the resulting snippet can be used directly in production without additional setup.