[ENH] Implement load_model function for ensemble classifiers

[inclinedadarsh]

Reference Issues/PRs

Fixes #2436

What does this implement/fix? Explain your changes.

Implement separate load_model function for ensemble models, which takes in model_path as list of strings and classes and loads all the models separately and stores them in self.classifiers_

Does your contribution introduce a new dependency? If yes, which one?

Nope.

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I have added the following labels to this PR based on the title: [ $\color{#FEF1BE}{\textsf{enhancement}}$ ].
I have added the following labels to this PR based on the changes made: [ $\color{#BCAE15}{\textsf{classification}}$ ]. Feel free to change these if they do not properly represent the PR.

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