Replace bsl::string with std to fix build error

[ahsanabbas123]

Problem Statement

Build was failing with the errors in rmqio_asioresolver.t.cpp

error: no matching constructor for initialization of 'entry_type' (aka 'basic_resolver_entry<boost::asio::ip::tcp>')
        entries.push_back(entry_type(endpoint, host, port));
                          ^          ~~~~~~~~~~~~~~~~~~~~
/boost/asio/ip/basic_resolver_entry.hpp:53:3: note: candidate constructor not viable: no known conversion from 'bsl::string' (aka 'basic_string<char>') to 'boost::asio::string_view' (aka 'basic_string_view<char>') for 2nd argument
  basic_resolver_entry(const endpoint_type& ep,
  ^

Proposed changes

Changing to std::string should fix build