[RedSuns Review]Add EfficientDet(Keras) Tutorial.

[ueno-hiroshi002]

Pull Request Description:

• Add EfficientDet(Keras) Tutorial, and model and utils sources.
• Add a link to this tutorial in task_notebooks/README.md.

Checklist before requesting a review:

• I set the appropriate labels on the pull request.
• I have added/updated the release note draft (if necessary).
• I have updated the documentation to reflect my changes (if necessary).
• All function and files are well documented.
• All function and classes have type hints.
• There is a licenses in all file.
• The function and variable names are informative.
• I have checked for code duplications.
• I have added new unittest (if necessary).

[ueno-hiroshi002]

The source files in the models directory have been classified and refactored according to the following criteria:

MCT original source (models/utils):

• Added comments following MCT rules
• Removed unnecessary code

External source (models/efficientdet):

• Removed unnecessary code (noted at the beginning)
• No additional comments