Lack of operators in string and string_view documentation

[karczex]

ISSUE: Lack of operators in string and string_view documentation

Environment Information

Webpage generated by Github actions CI

Please provide a reproduction of the bug:

https://pmem.io/libpmemobj-cpp/master/doxygen/classpmem_1_1obj_1_1basic__string__view.html
https://pmem.io/libpmemobj-cpp/master/doxygen/classpmem_1_1obj_1_1basic__string.html

Expected behavior:

All Non-member operators should be listed in documentation page. In general it should be similar to https://en.cppreference.com/w/cpp/string/basic_string Non-member functions section

[karczex]

It seems /relates <name> doxygen tag should resolve problem
https://www.doxygen.nl/manual/commands.html#cmdrelates