Allowing the FisherSky class to have angle unit suffix rad deg

[Thomas-JACQUOT]

This PR aims to allow FisherSky class to have angle unit suffix rad deg

Standard information about the request

This is a new feature, which make the FisherSky class able to deal with angle unit suffixes

This change will: change nothing in other parts of the code, it adds only a new feature for the FisherSky class.

Motivation

@titodalcanton, @pannarale and I wanted to change the [prior-ra+dec] section of GRBXXXX.ini files in order to be more clear (see discussion here). To do so, it needs to change the FisherSky class to make it able to deal with angle unit suffixes (just as @titodalcanton did here)

Contents

• The author of this pull request confirms they will adhere to the code of conduct

[titodalcanton]

After this change, angle_unit will no longer be necessary, so I suggest removing it. I do not think any analysis actually used FisherSky yet, so it should be ok to break backwards compatibility.

Also, you will have to rebase this on master after #4991 is merged for the tests to pass.

[titodalcanton]

Looks perfect, thanks.