Upgrade UncheckedExtrinsicV4 to V5

[Niederb]

Currently the nightly build is failing due to usage of two deprecated types.

• sp_runtime::traits::Extrinsic
• sp_runtime::traits::Extrinsic::SignaturePayload

Additionally it seems the SignedExtra type was removed

• solochain_template_runtime::SignedExtra

[haerdib]

ExtrinsicVersion was updated to Version 5:

• relevant code: https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/primitives/runtime/src/generic/unchecked_extrinsic.rs#L48
• PR: https://github.com/paritytech/polkadot-sdk/pull/3685/files#diff-7be1730dfe08652baee2cb237c2d33df42c5eb85408639864c6a4a9223f0ca32

I think the following must be done to close this task:

• Check if a simplified, self-defined Extrinsic is still needed or not (heavily dependent on the extrinsic_params.rs definitions)
• Deprecate the ExtrinsicV4 type
• : Introduce the ExtrinsicV5 type, by either (depending on the findings above):
  • introduce a new simplified V5 type
  • reexport the one from Parity, and make the V5 type the standard one.