Epic: {T346285}
== Background
In {T350495}, we deployed the latest version of the JS client library. We can now migrate the WikiLambda instrumentation to use core interaction events.
Since the the WikiLambda instrumentation has a lot of instrumentation-specific (domain-specific?) custom data, this will provide a good case study in creating and using a new schema that extends the core interaction event schema with the JS client library.
== AC
[v] ~~Wherever possible, the data logged by [[ https://codesearch.wmcloud.org/search/?q=dispatchEvent%5C%28&files=resources%5C%2Fext%5C.&excludeFiles=&repos=Extension%3AWikiLambda | the existing instrument ]] is mapped to the `{ action, action_subtype, action_source, action_context }` 4-tuple~~ (This approach was finally discarded)
[v] A new mapping strategy has been discussed and agreed: https://docs.google.com/spreadsheets/d/1WiPR-uzGlJ2LJ5DKks3WYRGV0W2uOl6l2WqwfdqZbrc/edit#gid=362321310 ('event flows 2.0' tab)
[] Repeated fields are identified and a schema fragment is created [[https://gerrit.wikimedia.org/r/c/schemas/event/secondary/+/992224|review]]
** e.g. `/fragment/mediawiki/wikilambda/common/1.0.0`
[] A new custom schema is created for this instrument [[https://gerrit.wikimedia.org/r/c/schemas/event/secondary/+/992224|review]]
** e.g. `/analytics/mediawiki/product_metrics/wikilambda/ui_actions/1.0.0`
[v] `active_browsing_session_token`has been added as a contextual attribute ({T358758})
[] The instrument code is updated to use the above (keeping the previous one for now) [[https://gerrit.wikimedia.org/r/c/mediawiki/extensions/WikiLambda/+/992226 | review ]]
[] The new stream configuration is added (keeping the previous one for now) [[ https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/992223 | review ]]