Some of them already go through features - for those we just rename the feature so that its name attribute is equal to the intended "optional" tag.

For the remaining ones, we add new Feature subclasses in new files src/sage/features/internet.py, mip_backends.py.

Follow-ups:

• sage.misc.latex: Replace have_... functions by Features #32650 latex.py,
• Features for interpreter interfaces #32866 interfaces.py,
• doctests: Detect "safe" external features even if "--optional=external" is not used #32174, in which we can deprecate the has_... functions

Depends on #30887
Depends on #32614

CC: @kwankyu @jhpalmieri @seblabbe @dimpase @jdemeyer @saraedum @tscrim @dcoudert @sagetrac-tmonteil @videlec

Component: refactoring

Author: Matthias Koeppe, Kwankyu Lee

Branch: 1d02bd0

Reviewer: Kwankyu Lee, Matthias Koeppe, Sébastien Labbé

Issue created by migration from https://trac.sagemath.org/ticket/32649