report: rename varlink dir for upload plugins

let's name the dir "/run/systemd/report.upload/" (rather than
"/run/systemd/metrics-upload/"). After all, these are reports that we
upload, not indiviudual metrics. And it would be particular confusing
since the dir to pick up metrics is called /run/systemd/report/, rather
than /run/systemd/metrics/. Hence the thing that deals with reports is
nmamed metrics, and the thing that deals in metrics is named reports...

man/systemd-report.xml

@@ -88,7 +88,7 @@
         to an external server. Two upload mechanisms are supported. If an <literal>http://</literal> or
         <literal>https://</literal> URL is specified with <option>--url=</option>, an HTTP upload will be
         performed to the specified location. Otherwise, any sockets under
-        <filename>/run/systemd/metrics-upload/</filename> will be used to call
+        <filename>/run/systemd/report.upload/</filename> will be used to call
         <function>io.systemd.Report.Uploader.Upload()</function>.</para>
 
         <para>Match expressions supported by <command>metrics</command> are supported here too.</para>

src/report/report.h

@@ -9,7 +9,7 @@
 #define REPORT_CERT_FILE     CERTIFICATE_ROOT "/certs/systemd-report.pem"
 #define REPORT_TRUST_FILE    CERTIFICATE_ROOT "/ca/trusted.pem"
 
-#define REPORT_UPLOAD_DIR "/run/systemd/metrics-upload"
+#define REPORT_UPLOAD_DIR "/run/systemd/report.upload"
 
 extern sd_json_format_flags_t arg_json_format_flags;
 extern char *arg_url, *arg_key, *arg_cert, *arg_trust;