Add mapstructure tags to echox.Config

[fmontorsi-equinix]

This PR makes it possible to include the echox.Config structure in the configuration structure passed to viper.UnmarshalExact().
This also aligns the echox.Config structure to the use of mapstructure tags like all other Config structures inside config.go files like:

• ./otelx/config.go
• ./ginx/config.go
• ./loggingx/config.go
• ./events/config.go
• ./crdbx/config.go
  Note that the naming of mapstructure tags has been aligned to match the corresponding naming in the pre-existing function MustViperFlags.

IMPORTANT: applications using the echox.Config structure should be reviewed to make sure they employ (in their configuration files) the exact syntax encoded in the mapstructure tags. For example if an application is exposing in its configuration file a parameter named 'shutdownGracePeriod', such parameter should be renamed to 'shutdown-grace-period' (this brings consistency with the viperx/cobrax bindings created by MustViperFlags method).

[fmontorsi-equinix]

@nicolerenee , @andy-v-h , @mikemrm ,
I wonder if you can review this PR and merge it as it's been waiting in the queue for so long... thanks