A new command to list and extract template files

[lunny]

When you want to customize your templates, you have to go to find source and download them. And also the same version. When you are in a stable version, you could find it easy. But for a dev branch, it's not as easy as before.

Since all templates has been embedded in binary, if we can list them and extract them. That's better.

update:

Maybe we could extract template files from a gitea sub command like

gitea resource list
gitea resource view templates/repo/migrating
gitea resource extract templates/repo/migrating

Then it will load the special template file from binary embbed resources to current directory.

update:
I rename template to resource so that we could also view/extract js/css files to inspect purpose.

[sapk]

Just for context, I will link the issue where this was also discussed: #9320 (comment)