[v2] Add support for optional fields for config struct

[yurishkuro]

Looking for a volunteer to add support for optional fields for config structs.

• Main issue: How to declare optional parts of the config? open-telemetry/opentelemetry-collector#10266
• Prototype: WIP do not merge - optional config fields open-telemetry/opentelemetry-collector#10260
• which is blocked by: Allow DecodeHook to run for zero values go-viper/mapstructure#37

Objective: create a draft PR with a prototype solution outlined in go-viper/mapstructure#37 (make sure it's a draft to avoid creating notifications noise to go-viper maintainers). Update this ticket with a link so that we can collaborate on that prototype.

[nag0yan]

@yurishkuro
Hello. Can I try this issue?

[yurishkuro]

You don't need to ask

[mahadzaryab1]

@yurishkuro opened a draft at go-viper/mapstructure#42. Let me know if you have any feedback and I'd be happy to incorporate it in.