Add support for GK-2B/GOCI2 data at L1b/c

[simonrp84]

This PR adds support for level 1 data produced by the GOCI-II ocean color instrument flying aboard GeoKompsat-2A.

Data is produced by the sensor in a series of sections that, together, cover either an area around Korea or the full disk. Each section is sensed at a different time. There is also a data product joining these sections together to create a full-area image at L1c.

Right now, this PR is a draft as: 1) I haven't added any tests 2) The full disk data is not read successfully. 3) I need to add a proper area definition, which should be possible from the L1 attributes (the data is in GEOS projection). Currently I cannibalised code from the L2 GOCI reader that generates a swathdefinition.

• [ ] Tests added
• [ ] Fully documented

[simonrp84]

pre-commit.ci autofix

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 27.86885% with 44 lines in your changes are missing coverage. Please review.

Project coverage is 95.85%. Comparing base (c9aabb7) to head (d5113c8). Report is 3 commits behind head on main.

:exclamation: Current head d5113c8 differs from pull request most recent head 6527d45. Consider uploading reports for the commit 6527d45 to get more accurate results

Files	Patch %	Lines
satpy/readers/goci2_l1_nc.py	27.86%	44 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2796 +/- ## ========================================== - Coverage 95.95% 95.85% -0.10% ========================================== Files 379 380 +1 Lines 53861 53922 +61 ========================================== + Hits 51680 51686 +6 - Misses 2181 2236 +55 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2796/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [behaviourtests](https://app.codecov.io/gh/pytroll/satpy/pull/2796/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.08% <0.00%> (-0.01%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2796/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `95.94% <27.86%> (-0.10%)` | :arrow_down: | 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=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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