Rename the task `load_file`

[tatiana]

trafficstars

Please describe the feature you'd like to see Since Astro 0.7.0, load_file can be used to load multiple files, as opposed to a single one. The name should be consistent with this behavior.

Describe the solution you'd like Rename the task load_file to load.

Are there any alternatives to this feature? An alternative name to load could be extract.

Additional context There have been internal discussions about how we should name both the load and save operations. We are still in a position where we can introduce breaking changes.

Acceptance Criteria

• [ ] All checks and tests in the CI should pass
• [ ] Update example DAGs
• [ ] Improve the documentation (README, Sphinx, and any other relevant) /postgres_operator_howto_guide.html))