build: derive version from Git tag via axion-release plugin (#50)

* build: derive version from Git tag via axion-release plugin

Replace hardcoded version = '0.1.0' with scmVersion.version from the
pl.allegro.tech.build.axion-release plugin. Tag prefix is set to empty
string to match existing plain-semver tags (e.g. 0.1.1, not v0.1.1).

On a tagged commit the version resolves to the exact tag; on subsequent
commits it becomes a SNAPSHOT (e.g. 0.1.2-SNAPSHOT), removing the need
to manually update build.gradle before each release.

Signed-off-by: Jimisola Laursen <jimisola@jimisola.com>

* build: use simple versionCreator to avoid branch name in snapshot version

Signed-off-by: Jimisola Laursen <jimisola@jimisola.com>

---------

Signed-off-by: Jimisola Laursen <jimisola@jimisola.com>

Author: jimisola

build.gradle

@@ -4,10 +4,18 @@ plugins {
     id 'maven-publish'
     id 'io.spring.javaformat' version '0.0.47'
     id 'com.gradle.plugin-publish' version '2.1.1'
+    id 'pl.allegro.tech.build.axion-release' version '1.18.0'
+}
+
+scmVersion {
+    tag {
+        prefix = ''
+    }
+    versionCreator 'simple'
 }
 
 group = 'io.github.reqstool'
-version = '0.1.0'
+version = scmVersion.version
 
 java {
     sourceCompatibility = JavaVersion.VERSION_21