add `last_updated_time_in_index` to `retrieve_dataframe`

[KristianVangsnes]

Description

Adding last_updated_time_in_index to retrieve_dataframe function, which makes index into multi-index. Also updated docstring.

Checklist:

• [x] Tests added/updated.
• [ ] Documentation updated. Documentation is generated from docstrings - these must be updated according to your change. If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• [ ] Changelog updated in CHANGELOG.md.
• [ ] Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.06%. Comparing base (91c82e6) to head (6d17c01).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1846 +/- ## ======================================= Coverage 91.05% 91.06% ======================================= Files 124 124 Lines 19245 19247 +2 ======================================= + Hits 17524 17527 +3 + Misses 1721 1720 -1 ``` | [Files](https://app.codecov.io/gh/cognitedata/cognite-sdk-python/pull/1846?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cognitedata) | Coverage Δ | | |---|---|---| | [cognite/client/\_api/raw.py](https://app.codecov.io/gh/cognitedata/cognite-sdk-python/pull/1846?src=pr&el=tree&filepath=cognite%2Fclient%2F_api%2Fraw.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cognitedata#diff-Y29nbml0ZS9jbGllbnQvX2FwaS9yYXcucHk=) | `89.12% <100.00%> (+0.09%)` | :arrow_up: | | [cognite/client/\_version.py](https://app.codecov.io/gh/cognitedata/cognite-sdk-python/pull/1846?src=pr&el=tree&filepath=cognite%2Fclient%2F_version.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cognitedata#diff-Y29nbml0ZS9jbGllbnQvX3ZlcnNpb24ucHk=) | `100.00% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/cognitedata/cognite-sdk-python/pull/1846/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=cognitedata)

[KristianVangsnes]

Where would be best to add the test? tests_unit/test_api/test_raw.py?

[haakonvt]

Where would be best to add the test? tests_unit/test_api/test_raw.py?

Yup!