Better explain the core dfuse features

[tehlowkeywiz]

To better reflect our new website structure, each "core feature" should have a dedicated section in the docs with examples to better expand on what these features are, use cases and examples on how to use them.

e.g. State
Lifecycle
Search
Push Guarantee

The website will have 1 page per feature, explaining the feature and linking to the docs where that feature is explained in more technical details.