Fix formatting of cice grid file

[anton-seaice]

This PR fixes two issues:

• In CICE6, angle of t-cell is called anglet however in the cice5-auscom build, we called this angleT.
• To make it easier to combine this file with cice history output, use names ni, nj for x and y dimensions. In conjunction with https://github.com/COSIMA/MOM6-CICE6/pull/54, this should allow a straight / no-warnings xr.merge of the grid with history output. Thanks to @aidanheerdegen for the suggestion.

Closes #16

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 6.66667% with 14 lines in your changes are missing coverage. Please review.

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:exclamation: Current head 569849e differs from pull request most recent head 5a71eae. Consider uploading reports for the commit 5a71eae to get more accurate results

Files	Patch %	Lines
esmgrids/cice_grid.py	8.33%	11 Missing :warning:
esmgrids/cli.py	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #18 +/- ## ====================================== Coverage ? 3.38% ====================================== Files ? 20 Lines ? 1241 Branches ? 0 ====================================== Hits ? 42 Misses ? 1199 Partials ? 0 ```

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[anton-seaice]

@dougiesquire apologies for the many reviews. please look at #17 first.