Better Type Annotations for Realtime Subscriptions

[Marviel]

Proposed type addition mockup:

export type ColNames = "name" | "type" | "unit" | "value" | "description";
export type FilterOps = "eq" | "ne" | "gt" | "lt" | "ge" | "le";
export type FilterType = `${ColNames}.${FilterOps}=${string}`;

// works!
const works1: FilterType = "name.eq=hello";
// typeerror (non existent column)
const fails1: FilterType = "name.eq=non-existent-column";
// typeerror (bad syntax)
const fails2: FilterType = "name.eq!!!hello";

It would be nice if the realtime subscription string type could be updated to reflect this.

I would submit a full PR except that I think this has implications for some other template types, which I don't have the personal time to dig into right now.