doc: Improve documentation on Telemetry Filters

[fgheysels]

The documentation on Telemetry Filters now describes how you can define such a filter, but it doesn't mention what that filter does (at least, not very specific.) It just says 'it allows you to filter out specific telemetry.

What exactly is meant to be ? Is it just something that makes sure that f.i. no Events are logged ? Or does it work in conjunction with the filter-levels ?
Why would I want to use it ?

[stijnmoreels]

What exactly is meant to be ? Is it just something that makes sure that f.i. no Events are logged ? Or does it work in conjunction with the filter-levels ?

To filter out certain telemetry types. Just like you would change the level on which log messages should be passed to the sinks, provides the telemetry filter a more surgical way to filter out certain telemetry types from the logging. Mostly, this is used for cost reduction, I imagine.

Why would I want to use it ?

In certain scenario's you want to filter out certain types to reduce costs. Saw scenario's where container logs where filtered on Metrics, Dependencies and Requests, for example