Option for case insensitive glossary references (without supressing all term warnings)

[ideasman42]

Previously the glossary in sphinx was case insensitive, so foobar would properly link to Foobar in the glossary.
In sphinx-build 3.0.3 we're getting many warnings:

manual/addons/materials/material_library.rst:41: WARNING: term fake user not found in case sensitive match.made a reference to Fake User instead.
manual/animation/actions.rst:84: WARNING: term walk cycle not found in case sensitive match.made a reference to Walk Cycle instead.
manual/animation/armatures/bones/editing/bone_roll.rst:10: WARNING: term Euler rotation not found in case sensitive match.made a reference to Euler Rotation instead.
manual/animation/armatures/posing/bone_constraints/inverse_kinematics/spline_ik.rst:53: WARNING: term roll not found in case sensitive match.made a reference to Roll instead.
manual/animation/constraints/interface/common.rst:20: WARNING: term object origin not found in case sensitive match.made a reference to Object Origin instead.
manual/animation/constraints/interface/common.rst:22: WARNING: term mesh not found in case sensitive match.made a reference to Mesh instead.
manual/animation/constraints/interface/common.rst:22: WARNING: term lattice not found in case sensitive match.made a reference to Lattice instead.
manual/animation/constraints/interface/common.rst:34: WARNING: term head not found in case sensitive match.made a reference to Head instead.
manual/animation/constraints/interface/common.rst:34: WARNING: term tail not found in case sensitive match.made a reference to Tail instead.
manual/compositing/types/color/z_combine.rst:39: WARNING: term Anti-Aliasing not found in case sensitive match.made a reference to Anti-aliasing instead.
... snip ... (over 100 of these)

Describe the solution you'd like
An option to use case insensitive references without warning.

Describe alternatives you've considered

• suppress_warnings = ["ref.term"] this suppresses all warnings, including references to non-existent glossary references (making this an impractical option).
• Adding different cases to the glossary, however this adds quite a bit
  of redundancy with no real benefit.

Additional context

The current glossary we're maintaining https://docs.blender.org/manual/en/dev/glossary/index.html

[tk0miya]

Finally, I determined to support case insensitive search officially. So warnings will not be shown.