Conan support for userver with ci

[xakod]

Introduce conan package as #119
Diffs from another pr:

• Do not change anything in source
• Instead of directly changes in source pr introduces another way: patch sources (it's how conan-center-index packaging works). Patch contains only changing packages names and prefer conan packages over source tree thirdparty packages.
• Gihub actions

Why patch? As previosly was said there is no current plans to change package naming so I decided do not modify source tree and proposed patch for conan.

Features

Core library building

• Stacktrace support
• Mongodb feature
• Postresql feature
• Postresql-extra feature (there is no cci package krb5, [request] krb5/1.18.3 conan-io/conan-center-index#4102)
• Redis feature
• Clickhouse feature (there is no cci package)
• GRPC feature
• RabbitMQ feature
• Universal feature

Current problems

Userver conan package as one monolithic package (userver for cmake for example) instead of

Finally, big thanx to @JorgenPo

[apolukhin]

Looks very good! Many thanks!

We'll merge it soon, we have to deal with some internal testing issues first