-- experimenting with metrics creation and collection

[VDanielEdwards]

Subject

Experimenting with creation, sending, and collection of various metrics.

The metrics can be used to get insights into internal behavior of individual SIL Kit participants or simulations.

Currently available metrics:

• COUNTER: Collects single unsigned integer value.
• STATISTICS: Collects single double values and accumulates minimum, maximum, exponential incremental mean, and standard deviation.
• STRING_LIST: Collects a list of strings.

If metrics are sent to remote participants, the participant that collects these, should be started first.

Collection and storage of the metrics is configured via the participant configuration file.

Metrics are only sent if they have changed.

Instructions for review / testing

Developer checklist (address before review)

• [ ] Changelog.md updated
• [ ] Prepared update for depending repositories
• [ ] Documentation updated (public API changes only)
• [ ] API docstrings updated (public API changes only)
• [ ] Rebase → commit history clean
• [ ] Squash and merge → proper PR title