`chain-spec`/presets reference docs added (#4678)

Added reference doc about:
- the pallet genesis config and genesis build, 
- runtime `genesis-builder` API,
- presets,
- interacting with the `chain-spec-builder` tool

I've added [minimal
runtime](https://github.com/paritytech/polkadot-sdk/tree/mku-chain-spec-guide/docs/sdk/src/reference_docs/chain_spec_runtime

)
to demonstrate above topics.

I also sneaked in some little improvement to `chain-spec-builder` which
allows to parse output of the `list-presets` command.

---------

Co-authored-by: Alexandru Vasile <[email protected]>
Co-authored-by: Sebastian Kunert <[email protected]>