[FEATURE] Support passing extra options to storage

[hauleth]

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

I want to use Peep's feature of global tags to store some global labels in each of the exported metrics. But unfortunately PromEx do not support any form of passing additional options to the storage without writing one manually, which seems to be a little bit wasteful.

Describe the solution you would like to see

Option to be able to pass extra options to the storage initialisation. Support for the global labels would be handy as well.

How would you expect this feature to work

Allow passing storage configuration options somehow. It also need to be possible to do dynamically, not just via static configuration, as some options (like global labels) can be set only during runtime (before PromEx startup, but still, not via compile-time only configuration).