Add AUTHORS and .mailmap

[julianbrost]

Generated using:

git log --format='format:%aN <%aE>' | grep -vFx 'dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>' | sort -u > AUTHORS

@Al2Klimov @raviks789 I've made the (non-)abbreviation of your names consistent with the Icinga DB AUTHORS file, please let me know if you prefer something different.

[raviks789]

Generated using:

git log --format='format:%aN <%aE>' | grep -vFx 'dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>' | sort -u > AUTHORS

@Al2Klimov @raviks789 I've made the (non-)abbreviation of your names consistent with the Icinga DB AUTHORS file, please let me know if you prefer something different.

Looks good to me.

[oxzi]

Reproduced the AUTHORS file successfully.