Create a demo to showcase new telemetry feature

[darthez]

This issue is depends on #905. Once telemetry work is completed we would like to create a demo that illustrates the integration of a Membrane pipeline with a tool like Prometheus.

The expected outcomes of this work are:

• code example as described above
• short video clip so it can be posted with the release notes on social media. Here is an example of such a clip - https://x.com/swmansion/status/1869778820016001130

[wende]

Using fly.io^[0] there's already a Grafana/Prometheus stack inbuilt out of the box.
Although there is no way to add new data sources (like Grafana Tempo) which would allow for easier processing of Telemetry span formats ^[1], I was able to manually format data so that it is displayed in Grafana Tempo format (picture below)

Given how easy it is to consume telemetry data with libraries like prom_ex^[2], I think this is the right way to go forward. At the same time it might allow us to be added to prom_ex available plugins list and gain some additional outreach quid pro quo

Prom_ex also aggregates the gathered telemetry data using telemetry_metrics^[3], so it resolves the issue of having only raw data and no meaningful data aggregation.

Using the tools above should allow us to both demonstrate the features of Membrane.Telemetry as well as be somewhat familiar to an average Elixir developer due to the usage of rather popular tools (Fly.io, Prometheus, Grafana) being all industry-standard solutions

[wende]