Skip rerank tests in mixed clusters (#126415)

If the clusters don't support inference test services, skip tests that require inference services.
Hence, we should check for rerank tests.

Relates #123074

Author: dnhatn

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/EsqlSpecTestCase.java

@@ -184,7 +184,7 @@ public final void test() throws Throwable {
     }
 
     protected void shouldSkipTest(String testName) throws IOException {
-        if (testCase.requiredCapabilities.contains("semantic_text_field_caps")) {
+        if (testCase.requiredCapabilities.contains("semantic_text_field_caps") || testCase.requiredCapabilities.contains("rerank")) {
             assumeTrue("Inference test service needs to be supported for semantic_text", supportsInferenceTestService());
         }
         checkCapabilities(adminClient(), testFeatureService, testName, testCase);

x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.g4

@@ -86,6 +86,7 @@ CHANGE_POINT : 'change_point' -> pushMode(CHANGE_POINT_MODE);
 // Once the command has been stabilized, remove the DEV_ prefix and the {}? conditional and move the command to the
 // main section while preserving alphabetical order:
 // MYCOMMAND : 'mycommand' -> ...
+DEV_COMPLETION : {this.isDevVersion()}? 'completion'      -> pushMode(EXPRESSION_MODE);
 DEV_INLINESTATS :  {this.isDevVersion()}? 'inlinestats'   -> pushMode(EXPRESSION_MODE);
 DEV_LOOKUP :       {this.isDevVersion()}? 'lookup_🐔'     -> pushMode(LOOKUP_MODE);
 DEV_METRICS :      {this.isDevVersion()}? 'metrics'       -> pushMode(METRICS_MODE);