Docs re-organization (#34765)

* Docs re-organization

The second phase of the handbook involves linking over to the SDK
docs from the handbook site. Before we do this, the SDK documentation
needs a re-org and an update. This is a continuation of the re-org,
following the platform updates. Remaining: Zap, tools, examples, IDs.

Done in this PR:
- remove API - this is a 4 year old design doc for a test dispatch
system that was never implemented. This does not make sense to keep
in the docs folder since it gives the incorrect impression that
this system was implemented at some point. In reality, our testing
is quite different and is decently well documented in the testing section.

- rename discussion to product consideration. This contains only the
ipv6 considerations doc, which isn't a discussion. Instead, we're
going to use this location to land documents related to product
considerations that affect matter, but are provided outside of the SDK,
ex. required network stack support (current doc), and factory
considerations (coming later) for things like DACs, individually
provisioned values, QR codes, config options, certification
declaration inclusion, DCL.

- move designing cluster for testing and portability from testing to
cluster design - it just makes more sense there.

- Creating a tips and troubleshooting section to land small guides,
move in avahi troubleshooting and guide around discovery from a host computer.

- remove quick start guide - everything in here is outdated, we
have a getting started guide and a readme that covers all the
getting started material. Added references to that in the readme
-

* couple more refs

* remove readme

Author: cecille

docs/QUICK_START.md

@@ -2,6 +2,10 @@
 
 ## Building and Developing
 
+-   A quick start guide to building a demo application and controller is
+    available in the [Getting started](./getting_started/) guide
+-   A guide to new cluster and device type development is available in the
+    [New Cluster and Device Type Developement Guide](./cluster_and_device_type_dev/)
 -   Documentation about building from the command line can be found in
     [the build guide](guides/BUILDING.md)
 -   Documentation about running [cirque](https://github.com/openweave/cirque)