Add spring-context-indexer to speed up startup (#3185)

#### What type of PR is this?

/kind improvement
/area core
/milestone 2.2.x

#### What this PR does / why we need it:

See https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-scanning-index for more.

#### Special notes for your reviewer:

This might help a little, bu we have to.

#### Does this PR introduce a user-facing change?

```release-note
None
```

build.gradle

@@ -88,6 +88,7 @@ dependencies {
     testCompileOnly 'org.projectlombok:lombok'
 
     annotationProcessor "org.springframework.boot:spring-boot-configuration-processor"
+    annotationProcessor "org.springframework:spring-context-indexer:6.0.4"
 
     developmentOnly 'org.springframework.boot:spring-boot-devtools'