[question] package_type documentation is not precise enough (Conan 2.0)

Conan 2.0 documentation for [package_type](https://docs.conan.io/en/2.0-alpha/reference/conanfile/attributes.html#package-type) is not precise enough to actually inform users of the bahaviour.

Things to improve:
1. For each `package_type` describe precisely how those map to requirement traits. Otherwise users will not understand the behaviour.
So for example:
"Requiring a `static-library` will set `headers=True`, `libs=True`, `run=False` traits by default".
"Requiring a `shared-library` will set `headers=True`, `libs=True`, `run=True` traits by default".
2. Document the heuristics used by Conan to guess the `package_type` if it is not provided.
3. Document the heuristics used by Conan to guess the actual `library` type when `library` package type is used.
4. Document `package_id_modes` used for each package type.

- [X] I've read the [CONTRIBUTING guide](https://github.com/conan-io/conan/blob/develop/.github/CONTRIBUTING.md).