Add config options to prometheus exporter

[psx95]

Fixes #2453

Changes

Added the following optional configuration options (booleans) to the prometheus exporter:

• without_units : controls whether to add unit suffixes (e.g. _seconds) to the metric names.
• without_type_suffix: controls whether to add type suffixes (e.g. _total) to the metric names.

• [ ] CHANGELOG.md updated for non-trivial changes
• [X] Unit tests have been added
• [ ] Changes in public API reviewed