chore: add sbt-scalafmt plugin

- Add sbt-scalafmt 2.5.5 plugin to project/plugins.sbt
- Enables scalafmtCheckAll and scalafmtAll commands in sbt

Author: ahoy-jon

project/plugins.sbt

@@ -3,3 +3,4 @@ addSbtPlugin("org.foundweekends.giter8" % "sbt-giter8-scaffold" % "0.17.0")
 addSbtPlugin("com.codecommit"           % "sbt-github-packages" % "0.5.3")
 addSbtPlugin("com.github.sbt"           % "sbt-git"             % "2.1.0")
 addSbtPlugin("com.github.sbt"           % "sbt-dynver"          % "5.1.1")
+addSbtPlugin("org.scalameta"            % "sbt-scalafmt"        % "2.5.5")