fix(polkadot): upgrade to v1.2.0

[renauter]

Description

From previous PR https://github.com/threefoldtech/tfchain/pull/905:

• [x] Upgrade to Polkadot v1.2.0

  • [x] update versions of clap and serde_json dependencies
  • [x] add libp2p-identity dependency
  • [x] add block_relay to sc_service::build_network()
  • [x] pallet-smart-contract: use transfer_allow_death() instead of transfer()
  • [x] add sp-genesis-builder dependency
  • [x] implement sp_genesis_builder::GenesisBuilder<Block> for runtime

• [x] Complete PR https://github.com/threefoldtech/tfchain/pull/905 by adding:

  • [x] js client: use transferAllowDeath instead of transfer (see doc https://polkadot.js.org/docs/substrate/extrinsics/#balances)
  • [x] go client: use transfer_allow_death() instead of transfer()

About transferAllowDeath vs transferKeepAlive Some documentation on how account is reaped and can be reactivated https://medium.com/we-are-talisman/existential-deposit-1d3585e2d4d0

Related Issues:

• #906

Checklist:

• [x] My commits follow this conventional commits guide.