Add guage to track total stream size in bytes #161
Description
Is your feature request related to a problem? Please describe.
Good to have.
Describe the solution you'd like
Every time a chunk is written the gauge is incremented, every time a segment is deleted by retention it is decremented by the size of the segment. It also needs to initialised by the the writer and/or replicas.
Describe alternatives you've considered
..
Additional context
Decision: to include index files in the same gauge or track this separately.