Support dynamic loading of operators

[chenlica]

Different Texera deployments for scientific domains require different sets of operators. For instance, an operator of single-cell RNA sequence analysis is very valuable in the domain of bioinformatics, but the domain of Social Science does need it.

Currently the operators need to be decided when the entire system is compiled. Every time we add a new operator or modify an existing operator, we need to recompile the codebase.

What we need is the capability for the system to dynamically load a set of operators without compiling the system. Each deployment needs to specify a set of operators. When we start the engine, it will dynamically load these operators. We can even add new operators to a deployment without restarting the system.

To achieve the goal, I expect we need to use Java Reflection to dynamically loading a class.