Standardise non-negative integer weight dropdown across new issue form + board filter + sidebar

Problem

Follow-up from https://gitlab.com/gitlab-org/gitlab-ee/issues/3969#note_76280833

Decision

Standard text inputs in the issuable sidebar, in the issue creation screen, and in the issue boards scope filter get this dropdown to guide the users additionally:

This makes it similar to the due date field in the issue creation screen

This applies to:

• The issue page sidebar
• The board scope filter (supports the any function)
• New issue form

cc: @victorwu @dennis