Add support for tags, registry, image, and update_channel fields to app resources and data sources

[ewgenius]

This pull request introduces new fields to support enhanced configuration and metadata for Spice AI apps, both in the provider code and documentation. The main changes add support for specifying a custom container image, image registry, update channel, and arbitrary key-value tags for apps. These improvements are reflected across the Go client, Terraform provider, OpenAPI spec, and documentation.

Provider and API enhancements:

• Added support for registry, image, and update_channel fields in app configuration, allowing users to specify custom container images, registries, and update channels for deployments. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
• Introduced a tags field (map of string key-value pairs) for apps, enabling custom metadata and categorization. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Documentation updates:

• Updated documentation for data sources (app.md, apps.md) and resources (app.md) to describe the new registry, image, update_channel, and tags fields. [1] [2] [3]
• Extended OpenAPI schema and spec examples to include the new fields, with descriptions and example values. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
• Added a changelog entry documenting the introduction of these fields and their supported values.

Terraform provider implementation:

• Updated the provider's Go implementation to handle the new fields in data source models, schema definitions, and mapping logic, ensuring correct population and null handling for all new attributes. [1] [2] [3] [4] [5] [6] [7]

These changes collectively enable more flexible deployment options and improved app organization through tagging and custom image selection.