[master < T1220-MG] Fix bug on properties in c++ api

[antoniofilipovic]

This PR fixes few bugs:

• there was a problem with getting Properties - since std::string_view was used as a key to store Properties in std::map, due to the nature of how properties are retrieved from mgp_properties_get_next in combination with std::string_view, the new property would overwrite the old one and the user wouldn't get the correct state of properties (some would miss, std::map would be filled with same property)
• there was a missing set_property function in both mgp.hpp and _mgp.hpp

[master < Task] PR

• Check, and update documentation if necessary -> yes
• Update changelog -> still no
• Provide the full content or a guide for the final git message: Fix bug on (vertex|edge) properties in C++ API

[antepusic]

Good work! Would it make sense to replace string_view with string elsewhere in the API as well?

[antoniofilipovic]

Good work! Would it make sense to replace string_view with string elsewhere in the API as well?

Since there are no problems, I would leave it as is.

[antaljanosbenjamin]

Please see my comment about StealType.

[antepusic]

Looks good to go 🚀