Add ability to save whether or not an `iris` to `xarray` conversion happened in the decorators

[freemansw1]

Pulls code from #354 to allow developers to specify (with a new argument to the decorator irispandas_to_xarray) whether or not an iris->xarray conversion occurred, via a passed keyword argument.

Important note: I've now changed all of our decorators to allow keyword arguments. That means that when calling decorators in the future, you must call with an empty () regardless of whether or not you want to use them.

• [x] Have you followed our guidelines in CONTRIBUTING.md?
• [x] Have you self-reviewed your code and corrected any misspellings?
• [ ] Have you written documentation that is easy to understand?
• [x] Have you written descriptive commit messages?
• [ ] Have you added NumPy docstrings for newly added functions?
• [x] Have you formatted your code using black?
• [ ] If you have introduced a new functionality, have you added adequate unit tests?
• [x] Have all tests passed in your local clone?
• [ ] If you have introduced a new functionality, have you added an example notebook?
• [x] Have you kept your pull request small and limited so that it is easy to review?
• [x] Have the newest changes from this branch been merged?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.39623% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 57.05%. Comparing base (7ded724) to head (0800478). Report is 39 commits behind head on RC_v1.5.x.

Files	Patch %	Lines
tobac/utils/decorators.py	93.20%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## RC_v1.5.x #380 +/- ## ============================================= + Coverage 56.91% 57.05% +0.13% ============================================= Files 20 20 Lines 3440 3472 +32 ============================================= + Hits 1958 1981 +23 - Misses 1482 1491 +9 ``` | [Flag](https://app.codecov.io/gh/tobac-project/tobac/pull/380/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tobac-project) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/tobac-project/tobac/pull/380/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tobac-project) | `57.05% <93.39%> (+0.13%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tobac-project#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[github-actions[bot]]

Linting results by Pylint:

Your code has been rated at 8.72/10 (previous run: 8.72/10, +0.00) _{The linting score is an indicator that reflects how well your code version follows Pylint’s coding standards and quality metrics with respect to the RC_v1.5.x branch. A decrease usually indicates your new code does not fully meet style guidelines or has potential errors.}

[freemansw1]

@w-k-jones @snilsn I am ready for re-review when you are!

[freemansw1]

Ok, resolved that last comment. @w-k-jones, @snilsn ready to merge when you are.

[w-k-jones]

Great! Happy for this to be merged

[snilsn]

Great, please go ahead and merge! @freemansw1