Don't do a full page load when clicking Watch or Star (#29001)

- The watch/unwatch button and star/unstar get their own template
- The backend returns HTML instead of redirect

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Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>

templates/repo/watch_unwatch.tmpl

@@ -0,0 +1,14 @@
+<form hx-boost="true" hx-target="this" method="post" action="{{$.RepoLink}}/action/{{if $.IsWatchingRepo}}un{{end}}watch">
+	<div class="ui labeled button" {{if not $.IsSigned}}data-tooltip-content="{{ctx.Locale.Tr "repo.watch_guest_user"}}"{{end}}>
+		<button type="submit" class="ui compact small basic button"{{if not $.IsSigned}} disabled{{end}}>
+			{{if $.IsWatchingRepo}}
+				{{svg "octicon-eye-closed" 16}}<span class="text">{{ctx.Locale.Tr "repo.unwatch"}}</span>
+			{{else}}
+				{{svg "octicon-eye"}}<span class="text">{{ctx.Locale.Tr "repo.watch"}}</span>
+			{{end}}
+		</button>
+		<a hx-boost="false" class="ui basic label" href="{{.RepoLink}}/watchers">
+			{{CountFmt .Repository.NumWatches}}
+		</a>
+	</div>
+</form>