Support custom settings in Conan metadata

Description

In Add column in database to support new conan met... (!157481 - merged) we added the new columns to the packages_conan_metadata table to save package settings. Afterwards it was noticed that conan package might have custom package settings that an user wants to save.

Solution

• Delete existing columns os, architecture, build_type, compiler, compiler_version, compiler_libcxx and compiler_cppstd.
• Add new column conan_info of type jsonb to the packages_conan_metadata table in order to be able to save standard as well as custom package settings.
  • Add constraint to limit the length of column to 20_000 chars. This is what we already do for packages_npm_metadata link. We can tweak the limit if necessary in the future.