[clang-tidy] Add option to ignore capture default by reference in...

[clang-tidy] Add option to ignore capture default by reference in cppcoreguidelines-avoid-capture-default-when-capturing-this

The rule exists primarily for when using capture default
by copy "[=]", since member variables will be captured by
reference, which is against developer expectations.

However when the capture default is by reference, then there
is no doubt: everything will be captured by reference. Add
an option to allow just that.

Note: Release Notes do not need update since this check
has been introduced in the current WIP release.

A ticket has been opened at the C++ Core Guidelines repo
to consider updating the rule such that this behavior
is the default one:
https://github.com/isocpp/CppCoreGuidelines/issues/2060

Differential Revision: https://reviews.llvm.org/D147062