Add log_image for Tensorboard logger

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## 🚀 Feature

Currently Wandb and Neptune loggers have `.log_image()` method. It would be great to have the same method for Tensorboard also, so that we don't need to modify the code when changing the logger.

### Motivation

For quick experimentations, usually I start with Tensorboard logger first. Once the code is more stable and I want to do long-training, I switch to Wandb so that I can monitor the training progress remotely. Having the same method simplifies the user code.

### Pitch

Currently Tensorboard logger can log images by directly call the `.experiment.add_image()` method. The new `.log_image()` method would simply call this method.

### Alternatives

To handle different ways of logging images depending on the logger, user code either needs to (1) detect which logger is being used, and call the corresponding method to log images, or (2) override Tensorboard logger with the proposed change. Both options are not ideal.

### Additional context

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cc @borda @awaelchli @Blaizzy

Start at the Tensorboard logger entry point and compare the existing `.log_image()` methods in the Wandb and Neptune loggers. Trace how Tensorboard currently calls `.experiment.add_image()`, then make the new method provide equivalent logger usage and verify that image logging works through the common interface.

Written by the indexing model from the issue text.