Update to Polkadot-sdk 1.6.0

[gianfra-t]

Part of master ticket tasks/#419.

To perform the upgrade of Pendulum to Polkadot-sdk release 1.6.0 we need to update all the Spacewalk dependencies to polkadot-sdk release v1.6.0.

Note on extra dependencies

subxt and jsonrpc are two critical dependencies that we may want (or need) to update, depending on the common dependencies used also with polkadot-sdk.

polkadot-sdk released Jan 16, an idea would be to update subxt to v0.34.0 which released right after that. Consequently, jsonrpc could be bumped to 0.21 which is what subxt uses for that version. This may not be needed since we are already at v0.33.0 with subxt but is good to keep in mind, since hard-to-debug compilation errors may arise from these version definitions (see what happened here as described on PR description).

There are other jsonrpc imports which use a previous version and may require more refactor to upgrade, with low or no benefit.