add healthcheck end point

Add a /healthcheck end point, returning a simple JSON structure. Use a
template rather than normal JSON encoding to ensure that the template
engine is working correctly.

In the future, this could be extended to check that the API is
available, but for now a simple check that just the web server is
running is good enough.

lib/MetaCPAN/Web/Controller/Root.pm

@@ -93,6 +93,16 @@ sub robots : Path("robots.txt") : Args(0) {
     } );
 }
 
+sub healthcheck : Local : Args(0) {
+    my ( $self, $c ) = @_;
+
+    $c->res->content_type('application/json');
+    $c->stash( {
+        template => 'healthcheck.tx',
+        status   => 'healthy',
+    } );
+}
+
 =head2 end
 
 Attempt to render a view, if needed.

root/healthcheck.tx

@@ -0,0 +1 @@
+[% { status => $status }.json() | raw %]

t/controller/healthcheck.t

@@ -0,0 +1,19 @@
+use strict;
+use warnings;
+use lib 't/lib';
+
+use Cpanel::JSON::XS    qw( decode_json );
+use MetaCPAN::Web::Test qw( app GET test_psgi );
+use Test::More;
+
+test_psgi app, sub {
+    my $cb = shift;
+    ok( my $res = $cb->( GET '/healthcheck' ), 'GET /healthcheck' );
+    is( $res->code, 200, 'code 200' );
+    is $res->header('Content-Type'), 'application/json',
+        'correct Content-Type';
+    my $data = decode_json( $res->content );
+    is $data->{status}, 'healthy', 'has correct status';
+};
+
+done_testing;