Move version to a text file to ease backports and automation

Author: swallez

build.gradle.kts

@@ -19,7 +19,9 @@
 
 allprojects {
     group = "co.elastic.clients"
-    version = System.getenv("VERSION") ?: "7.x-SNAPSHOT"
+    // Release manager provides a $VERSION. If not present, it's a local or CI snapshot build.
+    version = System.getenv("VERSION") ?:
+        (File(project.rootDir, "config/version.txt").readText().trim() + "-SNAPSHOT")
 
     repositories {
         mavenCentral()

config/version.txt

@@ -0,0 +1 @@
+7.15.0