Create maven-metadata.xml for scala steward compatability

[er1c]

Ref:

• https://github.com/scala-steward-org/scala-steward/issues/1628
• https://maven.apache.org/ref/3.2.5/maven-repository-metadata/repository-metadata.html

Examples:

• https://repo1.maven.org/maven2/com/octopus/randomquotes/maven-metadata.xml
• https://github.com/coursier/coursier/issues/1874#issuecomment-783632512

[er1c]

Example failing test: https://github.com/tpunder/fm-sbt-s3-resolver/pull/65

[er1c]

This is passing in:

resolvers +=
  "Sonatype S01 OSS Snapshots" at "https://s01.oss.sonatype.org/content/repositories/snapshots"
addSbtPlugin("com.evenfinancial" % "fm-sbt-s3-resolver" % "0.21.0-SNAPSHOT")