Install `prometheus-cpp-dev` package instead of building source code

[fujitatomoya]

Minor install procedure update, and this is part of Ubuntu 22.04 support reminder.
Currently it only supports Ubuntu 20.04 so that prometheus-cpp-dev package cannot be installed from apt repository, given that tutorial explains and includes the procedure to build the prometheus-cpp-dev from the source code.
When we support Ubuntu 22.04, we can install with following.

apt install -y prometheus-cpp-dev

Probably version dependency could be introduced, so that specific version might needs to be tagged.

[fujitatomoya]

according to https://packages.ubuntu.com/search?keywords=prometheus-cpp-dev, prometheus-cpp-dev is not gonna be supported as debian package for ubuntu22. so i will go ahead to close this one for now. instead of this, we can go ahead with source build as we do with ubuntu20 right now.