feat: Set cache keys as span descriptions

[cleptric]

When possible, set the cache key as the span description when tracing the Symfony cache.

closes #619

[michaelzangerle]

Hey @cleptric. I stumbled upon the linked issue and your proposed solution looks nice. Any chance this gets merged soon?

[cleptric]

@michaelzangerle Would you mind trying it in one of your apps and reporting back?

[michaelzangerle]

@cleptric I just gave it a try and it already looks so much better and clearer in Sentry especially if you have very long list of cache get / save calls.

• Seeing CLASSMETADATA helps a lot
• I guess things like this rApp.Workflow.Config.Message.Response.WorkflowConfigResponse..id are related to the serializer and I have a lot of those in my traces (maybe there is a way to limit this)
• The only place where it still shows the span id seems to be when cache.save is called