[TASK] Add index to sys_category

All page, content and file-records TCEforms render a category 
tree in order to assign these. The tree building executes the 
same queries quite often. In order to optimize these queries
this change adds
* an index "category_parent" to sys_category.parent in order
  to for the parent category while index "parent" currently
  indexes the pid the record is stored.

* a combined index "category_list" to columns pid, deleted 
  and sys_language_uid.

Resolves: #54929
Releases: 6.2
Change-Id: I1d42ba7171dc1213d5d5559ae190092acaa57464
Reviewed-on: https://review.typo3.org/26775
Reviewed-by: Oliver Klee
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack