add type 'pom' and scope 'import' for grails-bom and jackson-bom

[jamesfredley]

These two BOMs were missing:

<type>pom</type>
<scope>import</scope>

Now they have type and scope and appear before spring-boot-dependencies

<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.apache.groovy</groupId>
        <artifactId>groovy-bom</artifactId>
        <version>${groovy.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
      <dependency>
        <groupId>com.fasterxml.jackson</groupId>
        <artifactId>jackson-bom</artifactId>
        <version>${jackson.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
      <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-dependencies</artifactId>
        <version>${spring-boot.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
....
</dependencyManagement>

this resolves the following on groovydoc task when spring-boot-dependencies is using a different Groovy Version.

Caused by: groovy.lang.GroovyRuntimeException: Conflicting module versions. Module [groovy-xml is loaded in version 4.0.25 and you are trying to load version 4.0.24