LightningCLI support for optimizers and schedulers via dependency injection

[mauvilsa]

What does this PR do?

Current LightningCLI's support for multiple optimizers and schedulers using dict as a type is a non-optimal solution. This pull request adds support for having a proper type hint for these kind of parameters and be in line with how multiple submodules work. The details are explained in the updates to the documentation.

Does your PR introduce any breaking changes? If yes, please list them.

None

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