HST Model loading does not merge DynamicParameters and FieldGroups correctly

In CMS-13875 the issue was fixed that deep copies of HstComponentConfigurations missed DynamicParameters and FieldGroups based on the order in which they were loaded.

After that fix, some integration tests started to fail.

This was related to the fix CMS-13875 however that fix was correct, but it triggered another loading issue of the DynamicParameters and FieldGroups : This time the merging of components related to DynamicParameters and FieldGroups is not correct.

Assume we have an abstract page setup as follows:

    /hst:hst/hst:configurations/unittestcommon/hst:abstractpages:
      jcr:primaryType: hst:pages
      /basepage:
        jcr:primaryType: hst:component
        hst:template: webpage
        /header:
          jcr:primaryType: hst:component
          hst:referencecomponent: hst:components/header
        /leftmenu:
          jcr:primaryType: hst:component
          hst:referencecomponent: hst:components/leftmenu

and

    /hst:hst/hst:configurations/unittestcommon/hst:components:
      jcr:primaryType: hst:components
      /header:
        jcr:primaryType: hst:component
        hst:componentclassname: org.hippoecm.hst.test.HeaderComponent
        hst:template: header
        /title:
          jcr:primaryType: hst:component
          hst:template: title

then obviously, when an hst:page references the hst:abstractpages/basepage, it should get a header with hst:componentclassname: org.hippoecm.hst.test.HeaderComponent but also the correct DynamicParameters and FieldGroups

It turned out that the classname and other fields were correctly merged, but not the DynamicParameters and FieldGroups .

This should be done in HstComponentConfigurationService#populateComponentReferences . In HstComponentConfigurationService#combine, the merging behavior must also be improved to do more finegrained merging instead of all-or-nothing