[Feature Request]: Multiple Treatment variables and multiple instrument variables in DoubleMLPLIV

### Describe the feature you want to propose or implement

Presently, I know that Multiple Treatment variables and multiple instrument variables in DoubleMLPLIV are possible, but is it possible to assign an instrument for a specific treatment variable when there are multiple treatments and multiple instruments?

### Propose a possible solution or implementation

_No response_

### Did you consider alternatives to the proposed solution. If yes, please describe

_No response_

### Comments, context or references

_No response_