### Check existing issues - [x] I've verified that this request isn't described by any existing issues. ### Request The confdb pydantic model needs support for filters with a new `parameters` entry. Example: ```yaml type: confdb-schema account-id: system name: snaps views: observe-plugs: parameters: status: summary: "Allows filtering snaps by status" presence: required-on-write plug: presence: optional ``` Where - `parameters` is optional - `summary` is optional - `presence` is optional and can be: - `required` - the parameter value must always be provided - `required-on-read` - must always be provided when reading - `required-on-write` - must always be provided when writing - `optional` - the parameter can be unconstrained in any request. This is the default value. - The confdb spread test should specify a simple filter to ensure it can be handled. - The snapd team should be asked to test before landing. source: [SD208](https://docs.google.com/document/d/1ykcf_J084vo_sAFA3kWO5UOvndOBhXs-gGx7Y_IvzoY/edit?tab=t.0) ### The problem it solves Allows filtering in confdb schemas.