[master < T1140] Add ToString for mgp::Value and all mgp types

[mpintaric55334]

[master < Task] PR

• Check, and update documentation if necessary
• Provide the full content or a guide for the final git message
  For util.md5 function in c++ util query module, a need for ToString method arised, so it was implemented.

To keep docs changelog up to date, one more thing to do:

• Write a release note here, including added/changed clauses
  Users can now call ToString() method on mgp::Value and Memgraph's data types when writing C++ query modules.
• Tag someone from docs team in the comments

[mpintaric55334]

@vpavicic will write documentation when PR is reviewed.

[antoniofilipovic]

Few comments, but good work

[antepusic]

Left a few comments. The suggestion to use string::append because the ToString methods build a std::string applies to all methods here.

[antepusic]

Looks pretty good! Left a few comments related to formatting and testing.

[antepusic]

I think we're good to go here 🚀
Left a small suggestion, but the PR is approvable either way.

[antoniofilipovic]

LGTG