add event logs to stf and db

[ecioppettini]

Implements parts of #390

There some missing parts still though:

• [x] Emitting the mqtt events.
• [x] Maybe expose some helper to use at the client side (although we may have this, I need to check)
• I'm not sure the current indexing make sense. We may want a composite index instead and always ask for all the indexed fields? But it's less versatile.
• The current rest interface has the issue that only 10 fields can be filtered. That said, I'm not sure how to this while leveraging pgtyped and checked arguments.
• [x] Also I imagine we want some block range size limitation.