Make YAML parser case-insensitive (with a warning message)

[AkihiroSuda]

Description

It might be less frustrating for users if we can make the YAML parser case-insensitive.

[afbjorklund]

I thought it was well-known, that YAML is both case-sensitive and whitespace-sensitive.

Maybe users shouldn't be exposed to all parts of it, and use flags or overrides instead ?

• https://github.com/lima-vm/lima/issues/545

I guess the "normal" solution is to generate the yaml instead, from code or from other markup.