Require additional user confirmation for making repo private (#36959)

To align with how GitHub requires additional explicit user interaction
to make a repo private, including informing them of implications on what
happens if they do.

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

templates/repo/settings/repo_name_confirm_fields.tmpl

@@ -0,0 +1,10 @@
+<div class="field">
+	<label>
+		{{ctx.Locale.Tr "repo.settings.enter_repo_name_to_confirm"}}
+		<span class="tw-text-red">{{.RepoName}}</span>
+	</label>
+</div>
+<div class="required field">
+	<label>{{ctx.Locale.Tr "repo.repo_name"}}</label>
+	<input name="repo_name" required maxlength="100">
+</div>