[Feature Request]: In IRM Model , allow for different learners for `g0` and `g1`

[PhilippBach]

Describe the feature you want to propose or implement

• The current interface is not flexible enough, e.g., to use pipeline based learners as for example in https://docs.doubleml.org/stable/examples/R_double_ml_pipeline.html

Propose a possible solution or implementation

• The more complex the pipeline learners get, the less flexible the current API appears. Currently we only allow for 2 learners for ml_g and ml_m which should also be provided as the default in the future, but add an option to add separate learners etc. for ml_g1 and ml_g0 if required

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

No response

Comments, context or references

No response