Moves REST endpoints for conversation messages into a separate controller for improved modularity and maintainability. Refactors logic to better support support-type conversations, removing unnecessary project_id handling and redundant code. Enhances separation between conversation and message operations.

Replaces ad-hoc exception handling with a centralized decorator,
introducing custom exceptions for unsupported conversation types.
Improves code clarity, reduces duplication, and ensures more
consistent HTTP error responses across conversation APIs.

Enables richer data storage for conversations by introducing a JSONB field for extra context.
Links products to support groups, improving flexibility in product support management via a new nullable foreign key.
Facilitates future enhancements in conversation and product handling.

Updates parameter names from 'type' to 'type_' in conversation-related functions to avoid shadowing built-in names and improve code readability.

Updates comments to more accurately describe API entrypoints,
improving readability and maintainability by aligning section
headers with their actual functionality.

Replaces ambiguous parameter name with a more explicit one to prevent confusion with the Python built-in type and improve code clarity.

Replaces use of 'in' operator with SQLAlchemy's 'in_' method
to ensure correct filtering of conversation types in queries.
Prevents potential logical errors and improves query reliability.

Clarifies validation error when a non-support conversation type
is provided, making the exception message more descriptive for
better debugging and user feedback.

Introduces the SUPPORT value to conversation types and updates REST API error handling for unsupported types.
Renames REST controller modules for consistency and registers their routes in the plugin.
Adds comprehensive unit tests for conversation endpoints, covering access control, validation, pagination, and error handling.
Facilitates future extension of conversation types and improves API reliability.

Relates to ITISFoundation/private-issues#51

Switches to using a query parameter utility for improved validation
and simplifies endpoint signatures. Updates OpenAPI spec to clarify
request body requirements and relaxes query param constraints to
offer greater flexibility in API usage.