[exporterhelper] Enable batching by default in a component

[mx-psi]

@mx-psi Thanks for the table; it was quite helpful.

While not entirely related with this PR, I realized that currently the configoptional flavours don't seem to handle providing an optional configuration that is enabled by default. For example, if an exporter wants to enable batching by default (as it is a better default for good performance for most exporters) and users can choose to disable batching if required, then there is no good way to do this without explicitly handling the nil case in the Unmarshal logic.

Does this make sense or am I misunderstanding the code? If it does make sense, do you think it is worthwhile to handle a case where batch is explicitly set to nil in the config definition?

Originally posted by @lahsivjar in #13865 (comment)

[mx-psi]

@mx-psi Thanks for the table; it was quite helpful.

While not entirely related with this PR, I realized that currently the configoptional flavours don't seem to handle providing an optional configuration that is enabled by default. For example, if an exporter wants to enable batching by default (as it is a better default for good performance for most exporters) and users can choose to disable batching if required, then there is no good way to do this without explicitly handling the nil case in the Unmarshal logic.

Does this make sense or am I misunderstanding the code? If it does make sense, do you think it is worthwhile to handle a case where batch is explicitly set to nil in the config definition?

Originally posted by @lahsivjar in #13865 (comment)

Yeah, in general we have no support for this (in configoptional or elsewhere). The proposed option of setting to nil would not work, since

sending_queue:
  batch:

is the same as

sending_queue:
  batch: null

And we have typically used empty-but-set to mean "please use the defaults".

The main thing we have discussed so far for supporting this is to have an 'enabled' field added to all optional sections. This could be done in the future (since the constructors for configoptional currently forbid having an 'enabled' field). That way you could do

sending_queue:
  batch:
    enabled: false

Would that solve your problem?

[lahsivjar]

Would that solve your problem?

Yeah, having an enabled option to control batching will definitely solve the problem.

[mx-psi]

Relevant search of where are we already using enabled as a field name: https://github.com/search?q=%28repo%3Aopen-telemetry%2Fopentelemetry-collector+OR+repo%3Aopen-telemetry%2Fopentelemetry-collector-contrib%29++%2F%60mapstructure%3A%22%28.%2B%2C%29%3Fenabled%28.%2B%2C%29%3F%22%60%2F+-path%3A%2F.*_test.go%2F+NOT+path%3A%2F%5Eservice%5C%2Ftelemetry%5C%2Finternal%5C%2Fmigration%5C%2F%2F&type=code