Add `ignore_initial_volumes` param to `ConfoundsCorrelationPlot`

[tsalo]

Related to https://github.com/nipreps/fmriprep/issues/2614. Once this is merged and there's a new release, I will open a PR to fMRIPrep.

Changes proposed:

• Add an ignore_initial_volumes parameter to the ConfoundsCorrelationPlot interface.
• Add an ignore_initial_volumes parameter to the confounds_correlation_plot function.
• Use the new parameter in related smoke tests.

[codecov[bot]]

Codecov Report

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

Comparison is base (546f143) 60.95% compared to head (b243fdf) 60.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #843 +/- ## ======================================= Coverage 60.95% 60.96% ======================================= Files 55 55 Lines 6557 6558 +1 Branches 954 954 ======================================= + Hits 3997 3998 +1 Misses 2374 2374 Partials 186 186 ``` | [Flag](https://app.codecov.io/gh/nipreps/niworkflows/pull/843/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps) | Coverage Δ | | |---|---|---| | [reportlettests](https://app.codecov.io/gh/nipreps/niworkflows/pull/843/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps) | `∅ <ø> (∅)` | | | [unittests](https://app.codecov.io/gh/nipreps/niworkflows/pull/843/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipreps) | `∅ <ø> (∅)` | | 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=nipreps#carryforward-flags-in-the-pull-request-comment) to find out more.

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[effigies]

@tsalo Can you duplicate this in nireports? https://github.com/nipreps/nireports/blob/main/nireports/interfaces/nuisance.py

[tsalo]

Can do!

[tsalo]

😱 I didn't actually use the parameter in this PR!!!