Add `BadgerDBListPipelines` method for `PipelineModel`

[jim-junior]

Description

Extend the PipelineModel struct by implementing a new standalone query method called BadgerDBListPipelines. To ensure backwards compatibility across current services and APIs, do not refactor, rename, or delete the legacy etcd-based ListPipelines implementation. This new addition introduces native support to perform a prefix scan and return a deserialized slice of all stored pipelines inside BadgerDB.

Requirements

• File Location: internal/models/pipeline.go
• Method Signature Strategy: Introduce a new method named BadgerDBListPipelines() ([]*types.Pipeline, error) on the PipelineModel struct.
• Transactionality: Perform the scan operation entirely inside a BadgerDB View (read-only) transaction boundary.
• Prefix Scanning Mechanics:
  • Create a database iterator using txn.NewIterator(badger.DefaultIteratorOptions).
  • Target keys matching the structural prefix: /pipelines/.
• Data Processing & Lifecycle Rules:
  • Iterate through matched items and extract the configuration payload using BadgerDB item lifecycle best practices (e.g., calling item.ValueCopy()).
  • Unmarshal each retrieved JSON payload back into a separate instance of types.Pipeline using the standard json.Unmarshal package.
  • Append pointers of these populated structures to a result slice.
• Error Handling: If no pipelines exist under the targeted namespace prefix, return an empty slice and a nil error to achieve functional consistency with how list variants typically drop out when no data is found.
• Testing: Author a dedicated unit test suite inside internal/models/pipeline_test.go to validate prefix parsing, payload unmarshaling, and array aggregation using an in-memory BadgerDB instance.

Success Criteria

• The BadgerDBListPipelines method is added cleanly to the model file without breaking the legacy codebase.
• Stored item iterations correctly utilize a read-only transaction iterator scoped precisely to the /pipelines/ byte boundary.
• Calling the listing method on an empty database successfully handles the fallback without dropping execution panics or unhandled errors.
• Test Case implementation: A comprehensive unit test is provided that:
  • Seeds an isolated, in-memory BadgerDB database with multiple disparate marshaled JSON pipeline mock structs.
  • Executes BadgerDBListPipelines and verifies that the output matches the expected length of seeded items.
  • Evaluates fields within the returned slice to guarantee that property fields match the source configurations exactly.