Inconsistent use of the terms 'annotation' and 'directive' in docs

### Acceptance Criteria

**As a** ytt user looking at the "When should I include a space in my ytt comment?" question in the faq
**I want** to see an answer explaining why some annotations use spaces and some don't.

**As a** ytt user looking at the docs
**I want** to search the docs for "spaces in annotations", "#@ overlay or #@overlay", or "When do include a space in my annotations?", and see a result pointing to a FAQ response answering the question.

**As a** ytt user looking at the docs
**I want** to search the docs for "templating directive", or "directive", and see a result pointing to [Text Templating](https://carvel.dev/ytt/docs/latest/ytt-text-templating/).

Additional doc fix:
In the [Known Limitations](https://carvel.dev/ytt/docs/latest/known-limitations/) it mentions a "templating directive", I think these references can be changed to "annotation".

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Original issue context:

It was pointed out on slack that in the [faq](https://carvel.dev/ytt/docs/latest/faq/#when-should-i-include-a-space-in-my-ytt-comment-does-it-matter-is-it-load-or--load-overlaymatch-or--overlaymatch) defines a clear boundary between annotations and directives. This definition is confusing and it contradicts how we define a [yaml annotation in the yaml primer doc](https://carvel.dev/ytt/docs/latest/yaml-primer/#annotating-yaml).

@ewrenn8 noted: "All `#@`'s are annotations, the `#@ 1+1` is just syntactic sugar for the full annotation `#@temeplate/code 1+1`"

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