chore: improve sentry sampling

[kanej]

Sample most traces as before (1 in development, 0.001 in production), but exclude the indexing trace, which won't be sampled.

Indexing happens once per session, and is being used to provide feature flag information. That info is significantly less useful if it is sampled.

The fine grained control is provided by swapping from a trace sampling rate to a trace sampling function, as described here: https://docs.sentry.io/platforms/javascript/guides/capacitor/configuration/sampling/#setting-a-sampling-function

[kanej]

We have opted to remove the feature flags from indexing.