Added handling of multiple age inputs from user

[RazaProdigy]

In this pull request, I have made improvements to the age input handling in the Age Progression AI code. The original code had a fixed set of target ages or accepted a single target age as a string. I've expanded the functionality to allow for the processing of multiple age inputs provided as a comma-separated list.

1. Handling Multiple Age Inputs: Instead of only accepting a single target age as a string, the code now accepts a comma-separated list of target ages. For example, you can provide "10,20,30" as the target_age input.

2. Dynamically Generating Age Transformers: With the ability to provide multiple target ages, the code dynamically generates AgeTransformer instances for each specified age. This allows for the processing of multiple age transformations in a single run.

3. Improved Output File Handling: The output file format is now determined based on whether a single age transformation or multiple transformations are requested. If only one transformation is requested, the output is saved as a PNG image. If multiple transformations or the "default" target age set is provided, the output is saved as a GIF animation.

Please review and merge this pull request to benefit from these improvements in age input handling. Thank you!