chore: publish to Maven Central

[4rthurRousseau]

This PR sets up the project for publication to Maven Central using the Librarian library (fixes #47).

I upgraded Librarian from 0.0.7 to 0.2.1 to use the latest publication API and target Maven Central (see GradleUp/librarian#55).

Following the upgrade, I had to change the Gradle task used to build Dokka documentation as Librarian switched from Dokkatoo to Dokka its 0.2.0 version (GradleUp/librarian#97).

Both LIBRARIAN_SONATYPE_USERNAME and LIBRARIAN_SONATYPE_PASSWORD secrets will probably need to be updated.

Important note :
I had to add the Dokka plugin to both sample-app-android and sample-app-shared due to it being applied inside the Librarian plugin. The build fails without it, but in the current state, the sample-app-shared and sample-app-android documentation are published with the library documentation.

I feel like it should not be necessary regarding the comment in the librarianModule extension method :

/**
* Only configure Dokka for projects that are published.
* This is because we don't want those in the aggregate KDoc output.
*/

I wonder if this has something to do with the Librarian.root method that seems to configure the Dokka aggregate using allprojects (without checking whether publication is enabled or not).

I'm not confident with the Librarian library, so let me know if I'm mistaken @martinbonnin ! 🙂

[martinbonnin]

Thanks for looking into this. Gradle aggregations are a massive pain... I'll dig more tomorrow.

[martinbonnin]

I ended up modifying librarian to explicitely list subprojects. This is not great but I don't think there is another way (see also Kotlin/dokka#4489).

Thanks for the nudge on this 🙏