How to declare a configuration in a profile based on the package name

On profiles section, the [variable declaration](https://docs.conan.io/en/latest/reference/profiles.html#variable-declaration) is well defined and related to a single package only:

```
[settings]
zlib:compiler=clang
```

However, for conf there is no documentation about:

https://docs.conan.io/en/latest/reference/profiles.html#tools-configurations

For instance, it could be:

```
boost.tools.build:jobs=2
```

Which means, for Boost package, Conan will automatically run only 2 jobs.

Related to https://github.com/conan-io/conan-center-index/pull/11588