feat: add isOutputStage and namespaces for operators COMPASS-5876

[mcasimir]

• introduce isOutputStage to identify stages that would write to an external collection or bucket
• Replace isDbOnly with a namespace enum since there are also stages that are specific to collection types
• few pass-by fixes to documentation / properties
• add test to enforce the shape of operator metadata

[lerouxb]

Did you change the code in compass that uses dbOnly?

[mcasimir]

I need this to be released first. I learned that we have also stages that would only work with certain types of collections, including stages that are "collection only" like $collStats, so probably this client code is easier:

const namespaceType = isTimeseries : TIME_SERIES ? Boolean(sourceName) ? VIEW : COLLECTION;

const stageOperators = filter((op) => op.namespaces.include(namespaceType)) ...