Improve some Forms (#24878)

Don't really know a better name for this. I've gone through some Forms
and added missing HTML attributes (mostly `maxlength`). I tried to fill
the Forms with dummy Data and see if Gitea throws a Error (e.g. maximum
length). If yes, I added the missing HTML attribute.

While working on this, I discovered that the Form to add OAuth2 Apps
just silently fails when filled with invalid data, so I fixed that too.

templates/user/settings/keys_ssh.tmpl

@@ -12,7 +12,7 @@
 			{{.CsrfTokenHtml}}
 			<div class="field {{if .Err_Title}}error{{end}}">
 				<label for="title">{{.locale.Tr "settings.key_name"}}</label>
-				<input id="ssh-key-title" name="title" value="{{.title}}" autofocus required>
+				<input id="ssh-key-title" name="title" value="{{.title}}" autofocus required maxlength="50">
 			</div>
 			<div class="field {{if .Err_Content}}error{{end}}">
 				<label for="content">{{.locale.Tr "settings.key_content"}}</label>