Docs: Fix broken links in contribute/backend/README.md (#92261)

Co-authored-by: Dave Henderson <dhenderson@gmail.com>

devenv/docker/blocks/collectd/README.md

@@ -30,7 +30,7 @@ Environment variables
   - Graphite prefix
   - Optional, defaults to collectd.
 - `REPORT_BY_CPU`
-  - Report per-CPU metrics if true, global sum of CPU metrics if false (details: [collectd.conf man page](https://collectd.org/documentation/manpages/collectd.conf.5.shtml#plugin_cpu))
+  - Report per-CPU metrics if true, global sum of CPU metrics if false (details: [collectd.conf man page](https://www.collectd.org/documentation/manpages/collectd.conf.html))
   - Optional, defaults to false.
 - `COLLECT_INTERVAL`
   - Collection interval and thus resolution of metrics

devenv/docker/blocks/webdav/README.md

@@ -1,6 +1,6 @@
 # README for the image storage WebDAV docker block
 
-This block is used for testing the [WebDAV](https://grafana.com/docs/grafana/latest/setup-grafana/configure-grafana/#external_image_storagewebdav) option for external image storage which is used in [alert notifications](https://grafana.com/docs/grafana/latest/alerting/manage-notifications/images-in-notifications/). This uses the simplest WebDav server that is still being maintained, a project called [Dufs](https://github.com/sigoden/dufs).
+This block is used for testing the [WebDAV](https://grafana.com/docs/grafana/latest/setup-grafana/configure-grafana/#external_image_storagewebdav) option for external image storage which is used in [alert notifications](https://grafana.com/docs/grafana/latest/alerting/configure-notifications/template-notifications/images-in-notifications/). This uses the simplest WebDav server that is still being maintained, a project called [Dufs](https://github.com/sigoden/dufs).
 
 ## Using Dufs