Fix examples for servers with varied build tools (#433)

If the Develocity server from which builds are being fetched contains
build scans of build tools other than Gradle, such as Maven, the
`gradleAttributes` model will be null. While the examples could check it
for null, filtering these out from the query is more efficient.

Author: gabrielfeo

examples/example-notebooks/MostFrequentBuilds.ipynb

@@ -114,7 +114,7 @@
     "val builds: List<GradleAttributes> = runBlocking {\n",
     "    api.buildsApi.getBuildsFlow(\n",
     "        fromInstant = 0,\n",
-    "        query = \"\"\"buildStartTime>-7d\"\"\",\n",
+    "        query = \"\"\"buildStartTime>-7d buildTool:gradle\"\"\",\n",
     "        models = listOf(BuildModelName.gradleAttributes),\n",
     "    ).map {\n",
     "        it.models!!.gradleAttributes!!.model!!\n",

examples/example-project/src/main/kotlin/com/gabrielfeo/develocity/api/example/analysis/MostFrequentBuilds.kt

@@ -27,7 +27,7 @@ suspend fun mostFrequentBuilds(
     // Fetch builds from the API
     val builds: List<GradleAttributes> = api.getBuildsFlow(
         fromInstant = 0,
-        query = """buildStartTime>$startTime""",
+        query = """buildStartTime>$startTime buildTool:gradle""",
         models = listOf(BuildModelName.gradleAttributes),
     ).map {
         it.models!!.gradleAttributes!!.model!!

examples/example-scripts/example-script.main.kts

@@ -38,7 +38,7 @@ val api = DevelocityApi.newInstance()
 val builds: List<GradleAttributes> = runBlocking {
     api.buildsApi.getBuildsFlow(
         fromInstant = 0,
-        query = """buildStartTime>-7d""",
+        query = """buildStartTime>-7d buildTool:gradle""",
         models = listOf(BuildModelName.gradleAttributes),
     ).map {
         it.models!!.gradleAttributes!!.model!!