Worktime tracking for the organization level (#19808)

Dear Gitea team,

first of all, thanks for the great work you're doing with this project.

I'm planning to introduce Gitea at a client site, and noticed that while
there is time recording, there are no project-manager-friendly reports
to actually make use of that data, as were also mentioned by others in
#4870 #8684 and #13531.

Since I had a little time last weekend, I had put together something
that I hope to be a useful contribution to this great project (while of
course useful for me too).

This PR adds a new "Worktime" tab to the Organisation level. There is a
date range selector (by default set to the current month), and there are
three possible views:

- by repository,
- by milestone, and
- by team member.

Happy to receive any feedback!

There are several possible future improvements of course (predefined
date ranges, charts, a member time sheet, matrix of repos/members, etc)
but I hope that even in this relatively simple state this would be
useful to lots of people.

<img width="1161" alt="Screen Shot 2022-05-25 at 22 12 58"
src="https://user-images.githubusercontent.com/118010/170366976-af00c7af-c4f3-4117-86d7-00356d6797a5.png">

Keep up the good work!

Kristof

---------

Co-authored-by: user <user@kk-git1>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

options/locale/locale_en-US.ini

@@ -54,6 +54,7 @@ webauthn_reload = Reload
 repository = Repository
 organization = Organization
 mirror = Mirror
+issue_milestone = Milestone
 new_repo = New Repository
 new_migrate = New Migration
 new_mirror = New Mirror
@@ -1253,6 +1254,7 @@ labels = Labels
 org_labels_desc = Organization level labels that can be used with <strong>all repositories</strong> under this organization
 org_labels_desc_manage = manage
 
+milestone = Milestone
 milestones = Milestones
 commits = Commits
 commit = Commit
@@ -2876,6 +2878,15 @@ view_as_role = View as: %s
 view_as_public_hint = You are viewing the README as a public user.
 view_as_member_hint = You are viewing the README as a member of this organization.
 
+worktime = Worktime
+worktime.date_range_start = Start date
+worktime.date_range_end = End date
+worktime.query = Query
+worktime.time = Time
+worktime.by_repositories = By repositories
+worktime.by_milestones = By milestones
+worktime.by_members = By members
+
 [admin]
 maintenance = Maintenance
 dashboard = Dashboard