Dedicated conan repository

[battlmonstr]

Rationale

Currently we use a public conan repository ("conan center").

Our conanfile.py modifies build configurations of some libraries which makes them incompatible with the official conan center configurations. In practice it means that instead of downloading precompiled libraries we have to rebuild them from source.
Example: boost

In addition, some libraries don't exist in conan center (or exist only for an older version), and we have to use git submodules, and build them from source.
Example: libtorrent, libff

Some libraries exist in conan center, but not of the latest version, and we have to be stuck on an old version, because we want precompiled libraries.
Example: grpc

conan center doesn't provide Linux arm64 binaries and have no plans to do so.

These issues of 3rd party libs can be solved eventually by a dedicated conan repository.

Scope

This issue is about investigating what hardware/software requirements are needed for a conan repository, and setting up a VM for it for future experiments. A "push" to that repository has to be protected by some authentication, but downloads can be public (anonymous).

When we have a VM, we need to learn how to use that repository: how to create packages there, and how to download them.

[battlmonstr]

CC @lystopad