Add sensitivity calculator tutorials for DC4

[GallegoSav]

I created 2 tutorials for making sensitivity estimation based on the full LH analysis. One is for an extended source and the other for a point source. In theory people could also try model which combined both type of sources.

This pr require my astromodel pr to be merged for using ExtendedSource_sensitivity.ipynb though.

[codecov]

Codecov Report

❌ Patch coverage is 82.75862% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.22%. Comparing base (6765236) to head (61cedf8).

Files with missing lines	Patch %	Lines
cosipy/threeml/custom_functions.py	82.75%	5 Missing ⚠️

Files with missing lines	Coverage Δ
cosipy/threeml/custom_functions.py	85.18% <82.75%> (-0.53%)	⬇️

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[israelmcmc]

Thanks @GallegoSav.

I know I still need to review #247, but even after I merged it it'll take some time before it's released. I'm thinking it would be better to copy-paste SpatialTemplate_2D_Healpix to cosipy for now, and make an issue reminding us to use the one in astromodels once it's released.

[GallegoSav]

@israelmcmc Good point, I added the class in cosipy and created the issue #510 .

[israelmcmc]

Thanks @GallegoSav!