Model: AppConfiguration model supports monitoring capability backed by Prometheus

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What would you like to be added?

Support monitoring capabilities that are based on Prometheus in AppConfiguration model. This includes:

Definition of front-end (customer-facing) model
Upgrade the corresponding back-end render/generator logic
Documentation updated to reflect the new front-end (customer-facing) model: How to use the new model, with all the fields and possible values

See the design doc here.

Why is this needed?

This is part of the upgrade to AppConfiguration model. This enables kusion to render Prometheus-related resources (or corresponding annotations that enables scraping) based on user input and supports the transition from the current Server model to AppConfiguration model

Acceptance Criteria

Kusion can properly produce a valid, rendered YAML containing one or more Prometheus-related resources (or corresponding annotations that enables scraping), based on the user input from the AppConfiguration model.
Documentations updated on Kusionstack.io.

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This is merged in #490