Extract common metrics and logging

[noise64]

Part of #173

Done:

• extracted common grpc tracing and metrics from worker-executor to golem-common
• added grpc tracing and metrics to worker service
• switch to structured logging in
  • golem-common
  • worker-service (except openapi)
• added spans to golem-common retry and worker-service call_executor
• extracted common log and config handling
  • logging now can be configured for stdout and file output separately
  • added config loader:
    • configs now derived from the config struct defaults; added missing defaults and aligned them with the current toml local defaults
    • added common command line options to dump the default (and custom examples for covering enum config cases) and the loaded configs as toml or env vars
    • to avoid drifting code defaults and toml values (and to cleanup obsolete ones) added cargo make command to generate configs and sample env vars
• added a new json formatter to flatten spans in logs:
  • spans are merged into the main message json object with the span name
  • in case of repeated spans only the last span is included
• logging env var handling is extracted to common place for the local test env lib and now tracing env vars are passed through to the local golem services (e.g. one can enable json logging to files while running integ tests)

Todo in folllow up PR:

• use structured logs everywhere
• use grpc tracing everywhere
• add OpenAPI tracing like we have for grpc

[vigoo]

I like the changes! :)