Patch the plugin.xml with readme description

[zhutmost]

As discussed in this issue, I added some code to enable automatic pluginXml patching.

Because JetBrains's org.jetbrains.changelog repository (link) is a Gradle plugin (which provides similar functions in the Gradle template), I use Laika to convert Markdown to HTML.

The main code is in project/Utils.sc. To keep compatibility, maybe you can comment out the last three lines in build.sbt (to disable the patchPluginXml task?) (but I never tried this.)

[zhutmost]

The second commit is about to create GitHub action workflows to run build and release automatically. If you think it is unnecessary, feel free to revert it.

[unkarjedy]

Because JetBrains's org.jetbrains.changelog repository (link) is a Gradle plugin (which provides similar functions in the Gradle template), I use Laika to convert Markdown to HTML.

In principle, we could still use it.
plugins.sbt

...
libraryDependencies += "org.jetbrains.changelog" % "org.jetbrains.changelog.gradle.plugin" % "2.2.0"
resolvers += MavenRepo("Gradle Plugins", "https://plugins.gradle.org/m2/")

Utils.scala

val readmeDescriptionMd = readmeContent.substring(startIndex + startMarker.length, endIndex).trim
org.jetbrains.changelog.ExtensionsKt.markdownToHTML(readmeDescriptionMd, "\\n")

That would allow us to reuse changelog construction logic in future (though not in this PR)

[zhutmost]

I made these changes:

1. According to your recommendation, I changed the dependency from Laika to changelog.
2. Move the readmeDescriptionExtract function to build.sbt to simplify directory structure.
3. Bump sbt to 1.10.0 and scala to 2.13.13