Client expose custom MarkerName for user

[zedongh]

Cadence client sdk now only support 4 fixed marker names:

const (
	sideEffectMarkerName        = "SideEffect"
	versionMarkerName           = "Version"
	localActivityMarkerName     = "LocalActivity"
	mutableSideEffectMarkerName = "MutableSideEffect"
)

Is it possible for user custom marker name to record some special useful information, such as workflow dsl step or workfow running state information to rebuild workflow diagram?

In our production use cases, to rebuild workflow diagram from current history events not convenient.