Add version info to build.gradle

I copied this approach from other plugin repos, for example
[common-utils][1].

[1]: https://github.com/opensearch-project/common-utils/blob/7736e080f9b0a2f6f2d9ad3b4272090b281ea8fa/build.gradle#L43-L52

Signed-off-by: Andrew Ross <andrross@amazon.com>

build.gradle

@@ -13,6 +13,8 @@ buildscript {
   ext {
     opensearch_group = "org.opensearch"
     opensearch_version = System.getProperty("opensearch.version", "3.0.0-SNAPSHOT")
+    isSnapshot = "true" == System.getProperty("build.snapshot", "true")
+    buildVersionQualifier = System.getProperty("build.version_qualifier", "")
   }
 
   repositories {
@@ -39,6 +41,17 @@ repositories {
   maven { url "https://aws.oss.sonatype.org/content/repositories/snapshots" }
 }
 
+allprojects {
+  group 'org.opensearch.index.codec.customcodecs'
+  version = opensearch_version.tokenize('-')[0] + '.0'
+  if (buildVersionQualifier) {
+    version += "-${buildVersionQualifier}"
+  }
+  if (isSnapshot) {
+    version += "-SNAPSHOT"
+  }
+}
+
 apply plugin: 'opensearch.opensearchplugin'
 apply plugin: 'opensearch.internal-cluster-test'