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>

templates/org/menu.tmpl

@@ -45,6 +45,11 @@
 			</a>
 			{{end}}
 			{{if .IsOrganizationOwner}}
+			<a class="{{if $.PageIsOrgTimes}}active{{end}} item" href="{{$.OrgLink}}/worktime">
+				{{svg "octicon-clock"}} {{ctx.Locale.Tr "org.worktime"}}
+			</a>
+			{{end}}
+			{{if .IsOrganizationOwner}}
 			<span class="item-flex-space"></span>
 			<a class="{{if .PageIsOrgSettings}}active {{end}}item" href="{{.OrgLink}}/settings">
 				{{svg "octicon-tools"}} {{ctx.Locale.Tr "repo.settings"}}