Refactor project export using datumaro.Tranform

[ActiveChooN]

My actions before raising this issue

• Read/searched the docs
• Searched past issues

@zhiltsov-max proposed the idea to use datumaro transformations in CVATProjectDataExtractor class to reduce the amount of duplicated code with CVATTaskDataExtractor. Rough class implementation can look like:

task_datasets = { task_id: make_task_dataset(task) for task_id, task in tasks }
# append name mangling and other transforms like
for task_id, task_dataset in task_datasets.items():
    task_dataset.transform('rename', ...)

dataset = Dataset.from_extractors(*task_datasets)

The custom transformer can be written for frame number merging and image names mangling

Originally posted by @zhiltsov-max in #3502 (comment)