feat(Traefik Proxy): add tracing.sampleRate

[slayne]

What does this PR do?

This PR adds the option to specify a tracing samplingRate in the chart values

Motivation

The tracing samplingRate was not exposed in the values, meaning that we have to specify it directly in CLI options if needed.
solves #1269

More

• Yes, I updated the tests accordingly
• Yes, I updated the schema accordingly
• Yes, I ran make test and all the tests passed

[mloiseleur]

Thanks for this PR.
It has been introduced in v3.0 so there's no need to add a version checker.
About implementation, the double layer with is kinda weird.
Wdyt of those two options:

1. Lazy option

{{- with .Values.tracing.sampleRate }}
[...]

2. Refactor option

{{- with .Values.tracing }}
[all options starting .Values.tracing]
{{- with .sampleRate }}
[...]