Add mentionable teams to tributeValues and change team mention rules to gh's style...

Add mentionable teams to tributeValues and change team mention rules to gh's style (#13198)

* Add mentionable teams to tributeValues

Signed-off-by: a1012112796 <1012112796@qq.com>
* Apply suggestions from code review

Co-authored-by: silverwind <me@silverwind.io>
* Change team mention rules to gh's style

* use org's avator as team avator in ui

Signed-off-by: a1012112796 <1012112796@qq.com>
* Update modules/markup/html.go

* Update models/issue.go

Co-authored-by: Lauris BH <lauris@nix.lv>
* Update models/issue.go

* fix a small nit and update test code

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: 6543 <6543@obermui.de>