IRF outputs for protons + electron A_eff need better HDUCLAS headers

[kosack]

Describe the bug

The proton and electron effective areas in the IRF output have the same format as the gamma-ray one, however they should be distinguished by HDUCLAS not just EXTNAME to allow gammapy to correctly find them.

Gammapy uses a function that loads these IRFs into classes that looks at the HDUCLAS headers, and not specifically the name of the HDU, so in the example below, it finds 3 Aeff IRFs.

To Reproduce
Steps to reproduce the behavior:

print(fits.info(irf_file))

No.    Name      Ver    Type      Cards   Dimensions   Format
  0  PRIMARY       1 PrimaryHDU       4   ()
  1  EFFECTIVE AREA    1 BinTableHDU     39   1R x 5C   [40D, 40D, 5D, 5D, 200D]
  2  ENERGY DISPERSION    1 BinTableHDU     45   1R x 7C   [40D, 40D, 30D, 30D, 5D, 5D, 6000D]
  3  PSF           1 BinTableHDU     47   1R x 7C   [40D, 40D, 5D, 5D, 100D, 100D, 20000D]
  4  BACKGROUND    1 BinTableHDU     39   1R x 5C   [20D, 20D, 5D, 5D, 100D]
  5  EFFECTIVE AREA PROTONS    1 BinTableHDU     39   1R x 5C   [40D, 40D, 5D, 5D, 200D]
  6  EFFECTIVE AREA ELECTRONS    1 BinTableHDU     39   1R x 5C   [40D, 40D, 5D, 5D, 200D]

from gammapy.irf import load_irf_dict_from_file

irfs = load_irf_dict_from_file(irf_file)
print(irfs)

more than one HDU of aeff type found
loaded the EFFECTIVE AREA HDU in the dictionary
more than one HDU of aeff type found
loaded the EFFECTIVE AREA HDU in the dictionary

{'aeff': <gammapy.irf.effective_area.EffectiveAreaTable2D at 0x17383ae90>,
 'edisp': <gammapy.irf.edisp.core.EnergyDispersion2D at 0x1738d9940>,
 'psf': <gammapy.irf.psf.table.PSF3D at 0x1738daea0>,
 'bkg': <gammapy.irf.background.Background2D at 0x17383b890>}

Here, the correct Aeff IRF is loaded, since gammapy by default only retains the first one, but the order should not be relied upon.

Expected behavior

Gammapy doesn't complain about the extra IRFs that it doesn't need to know about.

[maxnoe]

There is no mechanism in GADF to do this, so for now I would propose to strip the GADF related headers from these HDUs, as they are not gamma ray IRFs