feature: auto de-duplication of plugin configs during dump

[hbagdi]

decK should be able to automatically de-duplicate configuration of multiple plugin instances of same type.

#93 implements de-duplication in the file but a user has to manually create the file or move the relevant pieces in the YAML source.

With this feature, de-duplication would happen automatically.

Such a feature helps in maintenance, where a user can simply edit the configuration in one place, instead of repeating.