[json-rpc]: pcr2 changes not backward compatible for iota-sdk

[kodemartin]

Description

As reported by @alexsporn

iota-proxy uses the iota-sdk now to get the latest system state from the JSON-RPC and parse the validators and pending validators.
I think the change we did here is not really backwards compatible with e.g. current Testnet.

iota-json-rpc-api
    /// Return the latest IOTA system state object on-chain.
    #[method(name = "getLatestIotaSystemState")]
    async fn get_latest_iota_system_state(&self) -> RpcResult<IotaSystemStateSummaryV2>;

    /// Return the latest IOTA system state object on-chain (version 1).
    /// Requires the `client-target-api-version` header to be set into
    /// a value `< 0.11` during requests.
    #[method(name = "getLatestIotaSystemState", version <= "0.10.99")]
    async fn get_latest_iota_system_state_v1(&self) -> RpcResult<IotaSystemStateSummaryV1>;

iota-sdk:
    /// Get the latest IOTA system state object on-chain.
    ///
    /// Use this method to access system information, such as the current epoch,
    /// the protocol version, the reference gas price, the total stake, active
    /// validators, and much more.
    pub async fn get_latest_iota_system_state(&self) -> IotaRpcResult<IotaSystemStateSummary> {
        Ok(self
            .api
            .http
            .get_latest_iota_system_state()
            .await
            .map(Into::into)?)
    }

So basically the newer SDK cannot be used to target RPC with older versions or else it will fail parsing of the IotaSystemStateSummaryV2 with this:
Rpc(ParseError(Error("missing field safeModeComputationCharges", line: 1, column: 98140)))

Proposed solution

After discussing with @thibault-martinez and @alexsporn we decided on introducing a new get_latest_iota_system_state_v2 method to return the refactored IotaSystemStateSummary and let get_latest_iota_system_state return IotaSystemStateSummaryV1 to be backward compatible.

This implies that iota-sdk should resolve the node-software version before calling the proper method to get the latest iota system state. cc: @Thoralf-M