remove delegate_to configuration option from our DSL

[GustavoCaso]

What does this PR do?

In our initial discussion, we agreed that the delegate_to option's main functionality was not to cache the result when configuring. For that reason, renaming it to cache would express with more accuracy the intent of the option.

I started by renaming it, but after seeing how much the option code has evolved since the initial conversation with the introduction of precedence, parsing env vars, etc... While trying to rename it to cache I realized that it would be more complicated than it seems, more importantly we have no idea how an option would work using delegate_to in the current system.

For the reason outlined above I think is best to remove the option since no configuration definition is using it, and if we ever want to introduce the ability to configure if an option is cached we could do it in the future, hopefully with some requirements defined.

Motivation:

Additional Notes:

How to test the change?

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!