Publish Dokka docs in our `javadoc.jar` artifacts

[thunderbiscuit]

Our API docs artifact published with bdk-android is currently a Javadoc style website, whereas it should be a Kotlin/Dokka style website. See https://javadoc.io/doc/org.bitcoindevkit/bdk-android/latest/index.html, which pulls in and publishes automatically what's in the javadoc.jar artifact (see the files at https://repo1.maven.org/maven2/org/bitcoindevkit/bdk-android/2.3.0/).

This can be done by configuring the new publishing plugin I suggest we use in #952 like so:

configure(
    AndroidSingleVariantLibrary(
        javadocJar = JavadocJar.Dokka("dokkaGeneratePublicationHtml"),
        sourcesJar = SourcesJar.Sources(),
    )
)

See https://vanniktech.github.io/gradle-maven-publish-plugin/what/#android-library-single-variant.

[thunderbiscuit]

This is now done! You can find the docs live at https://javadoc.io/doc/org.bitcoindevkit/bdk-android/latest/index.html