Support setting tenant for self-profiling

[Proximyst]

Is your feature request related to a problem? Please describe.

Currently, self-profiling does not support setting the tenant ID. This means that when self-profiling is enabled in -target=all mode, we cannot set the ID to e.g. pyroscope / monitoring / whatever makes sense for the organisation.

Describe the solution you'd like

Today, we already have a self-profiling config stanza in the configuration file. We should add a tenant ID to this, retaining today's behaviour of using anonymous if left empty.

Describe alternatives you've considered

Another option could be to set a global default tenant ID for monitoring. I don't think this is a good idea as there are no other uses for this right now. If this were to be relevant later, the default of this option can adapt when a global default is specified.

Additional context

N/A

[itsHabib]

@Proximyst , gave it a go here: #4880 hoping this is what was intended.