Add APIs into Client/UnregisteredClient for triggerContinueAsNew and updateWorkflowConfig

[longquanzheng]

They are existing in iWF yaml but not yet exposed to SDK.
https://github.com/indeedeng/iwf-idl/blob/a7fb55597de5591fffa406b6b5f07d85fda4dfee/iwf.yaml#L365

https://github.com/indeedeng/iwf-idl/blob/main/iwf.yaml#L290