Router service model (start, reload, crashed, etc.)

[milyin]

Describe the feature

In order to properly manage zenoh routers in the pass, zenohd should be able to provide information about its status. E.g., correctly running, shutting down, configuration being reloaded, etc.

Primary goals:

plugins should report their status through admin space. The possible statuses are:

all ok

warning (e.g. something misconfigured, deafult parameter used)

fatal error (e..g. no sql server connection)

failed to load (e.g. dll not found, config error, etc)

subplugins (e.g. backedns of storage plugin) should report the status in the same way

Secondary goals

improve plugin load safety (better ABI compatibility check)

simplify plugin API

unify plugin API for pluigns and subplugins

[milyin]

duplicates #583, no need to have separate issue