build: add sbt-git plugin (dropped by sbt-ci-release 1.12.0)

sbt-ci-release 1.12.0 removed its bundled sbt-git dependency (sbt/sbt-ci-release#471), so GitVersioning used in build.sbt no longer resolves and project load fails (CI: 'not found: value GitVersioning'). Restore sbt-git 2.1.0 explicitly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jigarkhwar

project/plugins.sbt

@@ -1,4 +1,5 @@
 addSbtPlugin("io.gatling"     % "gatling-sbt"    % "4.18.4")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.12.0")
+addSbtPlugin("com.github.sbt" % "sbt-git"        % "2.1.0")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"   % "2.6.1")
 addSbtPlugin("org.scoverage"  % "sbt-scoverage"  % "2.4.4")