Add sorting to milestone page list of work items

Proposal

On the milestone page, e. g. https://.../groups/group1/-/milestones/2#tab-issues

for the list of work items

allow for sorting of them.

For us - just sort them by manual sorting (from general issue list view or issue boards) would be just fine.

More generally - maybe beneficial to offer more options - like created date resp. issue ID, issue title.