Basically combines all the recommended calls into one
`build_using_defaults()` call or `init_with_defaults()` when there are
some custom changes required.

This implements the `CheckMetadataHash` extension as described in
[RFC78](https://polkadot-fellows.github.io/RFCs/approved/0078-merkleized-metadata.html).

Besides the signed extension, the `substrate-wasm-builder` is extended
to support generating the metadata-hash.

Closes: #291

---------

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>