Missing Groovy engine in OSGi environment

Describe the bug

Using Groovy in OSGi environment throws FlowableException (Can't find scripting engine for 'groovy'). For example, the exception will be thrown when you use the following execution listener:

<flowable:executionListener event="start" class="org.flowable.engine.impl.bpmn.listener.ScriptExecutionListener">
    <flowable:field name="script">
        <flowable:string>execution.setVariable('foo', 'bar')</flowable:string>
    </flowable:field>
    <flowable:field name="language">
        <flowable:string>groovy></flowable:string>
    </flowable:field>
</flowable:executionListener>

Expected behavior

Groovy language can be used in OSGi environment.

Code

The Extender component tries to read the factory class from the first line of the corresponding Groovy configuration file (groovy-jsr223/javax.script.ScriptEngineFactory), but it is the license header.

https://github.com/flowable/flowable-engine/blob/356c0084c2c24e52f18bcac88e9e828f4b69ccae/modules/flowable-osgi/src/main/java/org/flowable/osgi/Extender.java#L371

Additional context

I'm using the following components:

flowable-engine-6.7.2
flowable-osgi-6.7.2
groovy-all-2.4.21

I will try to submit a pull request with the fix.

flowable / flowable-engine

Missing Groovy engine in OSGi environment #3841