HOLI-9733: introduce tracing with Sentry

See merge request app/holi-app-volunteering!52

* Every request creates it's own trace manually. Automatic instrumentation did not work here, so it
  did not suffice to just create spans and have Sentry auto-start or continue a trace. Therefore,
  Distributed tracing is probably not working yet with this commit.
* Every request to the database or the GeoAPI is wrapped inside a Sentry span.

HOLI-9835: redesign API to fix client-side caching issue

See merge request app/holi-app-volunteering!51

On client side, Apollo client normalizes caches. Because an entity returned by this API can be
contained in multiple query results (`engagementById`, `engagementRecommendations`, ...) the entity
contained therein must always be of the same shape. Otherwise, this can lead to client-side cache
updates resulting in unexpected UI updates.

This commit introduces the type `EngagementReco` as an envelope around the actual
`Engagement` entity. `EngagementReco` additionally contains the query-specific fields
`matchedTopics`, `matchedSkills` and `matchedGeoLocationDistanceInMeters`.

To be backwards-compatible

* the current `engagementRecommendations` query continues to
  return the current shape of data
* the newly introduced `engagementRecos` returns items of the new
  `EngagementReco` with the aforementioned match fields "removed" from the `Engagement` entity (undefined)

Clients must upgrade to `engagementRecos`. Thereafter, `engagementRecommendations` can
be removed and the `matched*` fields within the `Engagement` type as well.

HOLI-9797 liveness check

See merge request app/holi-app-volunteering!49

HOLI-9790: use separate fields for topics & skills

See merge request app/holi-app-volunteering!48

Helps to avoid:

- confusion on users side that the same field contains (potentially) different topics and skills slugs with different ordering, depending on how you query the resource
- potential client-side caching issues that would result out of differences depending on how a query was made.

HOLI-9608: query engagement by ID from DB instead of Voltastics API

See merge request app/holi-app-volunteering!47

HOLI-9693: retry geometry lookup using place name when receiving point

See merge request app/holi-app-volunteering!46

HOLI-9570: add endpoint to filter engagements from the DB by terms and location

See merge request app/holi-app-volunteering!44

Co-authored-by: Daniel Bimschas <daniel.bimschas@holi.team>