Make TS_VERSION_STRING overridable (#12217)

This patch (hat tip @cmcfarlen) makes TS_VERSION_STRING a
user-overridable value. This allows the user to specify an arbitrary
major.minor.micro version according to their organizational needs
via something like:

-DTS_VERSION_STRING="10.1.0.65"

Author: bneradt

CMakeLists.txt

@@ -29,7 +29,10 @@ project(ats VERSION 10.2.0)
 set(TS_VERSION_MAJOR ${PROJECT_VERSION_MAJOR})
 set(TS_VERSION_MINOR ${PROJECT_VERSION_MINOR})
 set(TS_VERSION_MICRO ${PROJECT_VERSION_PATCH})
-set(TS_VERSION_STRING ${TS_VERSION_MAJOR}.${TS_VERSION_MINOR}.${TS_VERSION_MICRO})
+set(TS_VERSION_STRING
+    ${TS_VERSION_MAJOR}.${TS_VERSION_MINOR}.${TS_VERSION_MICRO}
+    CACHE STRING "The version string"
+)
 math(EXPR TS_VERSION_NUMBER "${TS_VERSION_MAJOR} * 1000000 + ${TS_VERSION_MINOR} * 1000 + ${TS_VERSION_MICRO}")
 
 # We make this a cache entry so that it can be configured to different values