Flexible way to fill DATAMAX/MIN BUNIT EXPOSURE in FITS header keywords

[nicHoch]

so far only products with "count" data fill in this keywords in a usefull way. with this more flexible way of generating it should be much better to fill this keywords for deticated products

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 76.82119% with 35 lines in your changes missing coverage. Please review.

Project coverage is 75.82%. Comparing base (8146f04) to head (a4651d9).

Files with missing lines	Patch %	Lines
stixcore/products/level0/quicklookL0.py	68.57%	11 Missing :warning:
stixcore/products/level1/quicklookL1.py	66.66%	8 Missing :warning:
stixcore/products/level0/scienceL0.py	68.42%	6 Missing :warning:
stixcore/products/level1/scienceL1.py	66.66%	6 Missing :warning:
stixcore/products/level2/housekeepingL2.py	66.66%	3 Missing :warning:
stixcore/processing/find.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #393 +/- ## ========================================== + Coverage 75.75% 75.82% +0.06% ========================================== Files 68 68 Lines 7119 7250 +131 ========================================== + Hits 5393 5497 +104 - Misses 1726 1753 +27 ```

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[samaloney]

Ok normal test look good now but in the E2E tests at L1530 and L2008 don't seem related and are unexpected at least at first look.