Support Spring Boot apps with no explicit version config

test case:

    @Test
    fun `adds java version property if not present if spring-like parent`() = rewriteRun(
        pomXml("""
            <?xml version="1.0" encoding="UTF-8"?>
            <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
              <modelVersion>4.0.0</modelVersion>
              <groupId>org.sample</groupId>
              <artifactId>sample</artifactId>
              <version>1.0.0</version>
              
              <parent>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-parent</artifactId>
                <version>2.7.0</version>
              </parent>
              
            </project>
        """.trimIndent(),
            """
            <?xml version="1.0" encoding="UTF-8"?>
            <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
              <modelVersion>4.0.0</modelVersion>
              <groupId>org.sample</groupId>
              <artifactId>sample</artifactId>
              <version>1.0.0</version>
              
              <parent>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-parent</artifactId>
                <version>2.7.0</version>
              </parent>
              <properties>
                <java.version>11</java.version>
              </properties>
              
            </project>
        """.trimIndent()
        ) // fails with no change
    )

Spring Boot declares a java.version property, pre-wired into the maven-compiler-plugin config. This is a convenient, common pattern to manage a project's Java version, and our recipes support updating that property if present.

But, because Spring Boot provides a default value (1.8) for java.version, it's feasible for a Spring Boot app to have no explicit configuration for its Java version in its pom.xml. And in that case, the upgrade recipe will do everything but actually update the build's Java version. The test case above shows this.

The tricky part here is deciding how generic the solution should be -- eg:

• do we just check for the "hardcoded" spring-boot-starter-parent parent, or identify arbitrary (non-project) parents which declare java.version
• should we validate that project pom isn't already managing its java version a different way (ie no explicit maven-compiler-plugin config)
• should we enforce an opinion that projects with spring-like parents should only use the java.version property to manage the Java version

Start with the Kotlin rewriteRun test in the issue and inspect the existing recipes that update the java.version property. Determine how Spring Boot parent defaults should be handled alongside other Java-version configuration, then add coverage for the chosen behavior. Done means the provided test passes without breaking existing migration cases.