[Docs] Guide page about getting and setting field values

[juliendelort]

Something that people usually look for when using a forms library is being able to easily get and set field values, so we should have a page in the guide section for that.

Some topics that the page should cover:

• How do I initialize the form?
• How do I initialize the form with values resulting from an API call? (we can show how to do this with and without Tanstack Query)
• How do I set a single field vs the entire form (if it is possible to set all the fields at once)
• Will setting a new value programmatically trigger validation? If not, is there a way to trigger it?
• How do I retrieve the current value of a single field? Of the entire form? (not necessarily within a onchange/onblur callback but also by directly calling the form API object)
• How do I listen for changes?

[crutchcorn]

I like this idea and outline. Let's move forward with it