Reduce confusion with profile types in Pyroscope

[simonswine]

Pyroscope uses profile types as a quite prominent feature in API and UI. The same time we are hiding the full profile type many times. The full profile type contains:

 <name>:<sample-type>:<sample-unit>:<period-type>:<period-unit>

• <name> is a user supplied name and is set by the external label with name __name__. It is set on a per profile (pprof) basis. Examples:
  • memory
  • godeltaprof_memory
  • block
  • mutex
• <sample-type/unit> is the type and unit of the actual samples at play. Examples:
  • contentions:count
  • delay:nanoseconds
  • cpu:nanoseconds
  • alloc_space:nanoseconds
• <period-type/unit> is the type and unit for the whole profile (aka pprof). AFAIK we don't expose this anywhere and it should be ignored all together. Examples:
  • contentions:count
  • cpu:nanoseconds
  • space:bytes

Here is a list of full profile types in GL largest cells:

``` block contentions count contentions count block delay nanoseconds contentions count godeltaprof_block contentions count contentions count godeltaprof_block delay nanoseconds contentions count godeltaprof_memory alloc_objects count space bytes godeltaprof_memory alloc_space bytes space bytes godeltaprof_memory inuse_objects count space bytes godeltaprof_memory inuse_space bytes space bytes godeltaprof_mutex contentions count contentions count godeltaprof_mutex delay nanoseconds contentions count goroutine goroutine count goroutine count goroutines goroutine count goroutine count memory alloc_in_new_tlab_bytes bytes space bytes memory alloc_in_new_tlab_objects count space bytes memory alloc_objects count space bytes memory alloc_space bytes space bytes memory inuse_objects count space bytes memory inuse_space bytes space bytes mutex contentions count contentions count mutex contentions count mutex count mutex delay nanoseconds contentions count mutex delay nanoseconds mutex count process_cpu alloc_samples count cpu nanoseconds process_cpu alloc_size bytes cpu nanoseconds process_cpu cpu nanoseconds cpu nanoseconds process_cpu exception count cpu nanoseconds process_cpu lock_count count cpu nanoseconds process_cpu lock_time nanoseconds cpu nanoseconds process_cpu samples count milliseconds process_cpu samples count cpu nanoseconds ```

In order to simplify this I propose that we implement:

### Tasks
- [ ] Support 4 part `__profile_type__` as `block:contentions:count`, which ignores period unit/type.
- [ ]  Rewrite `__name__` during ingestion to ensure consistency
- [ ] Deprecate ProfileType call and arguments in favour of LabelValues / Series and LabelSelectors

[simonswine]

cc @petethepig from our conversation

[wang-qijia]

From the user's perspective, this implementation is meaningful and reduces cognitive load.