[8-h.] logging the start and end time of the step

Реализовать сохранение времени начала и окончания step и Job в манифест

Look for models related to 'step' and 'Job' in the codebase, likely in a 'manifest' module or app. The task is to add start and end time fields to these models and ensure they are saved. Check existing serializers and views for these models to understand the data flow. Running the test suite after changes will verify the implementation.

Written by the indexing model from the issue text.