Enhance MySQL datasource configuration?

[rmannibucau]

Feature

Hikari pool for myslq storage uses a partial configuration.

Rationale

When the environment has some network instability it is neat to be able to configure the pool accordingly (eviction config typically).

Note

What i'm not sure: should the datasource be configured using spring boot datasource and zipkin mysql datasource configuration ignored in such a case or should the conditional bean producer for mysql datasource be enhancement to support more configuration with the related env variables in zipkin-server-shared.yml.