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.

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Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>