DB: some missing indices

[rfc2822]

 w: [ksp] /home/runner/work/davx5/davx5/app/src/main/kotlin/at/bitfire/davdroid/db/Collection.kt:42: ownerId column references a foreign key but it is not part of an index. This may trigger full table scans whenever parent table is modified so you are highly advised to create an index that covers this column.
w: [ksp] /home/runner/work/davx5/davx5/app/src/main/kotlin/at/bitfire/davdroid/db/WebDavDocument.kt:33: parentId column references a foreign key but it is not part of an index. This may trigger full table scans whenever parent table is modified so you are highly advised to create an index that covers this column.

The collection field for the push topic should also have an index (maybe it already has).