website: replace absolute link to relative

While running the workflows on the community tools while backporting a
change from main, it failed since one link to developer.hashicorp.com
was absolute.

To fix this workflow, we replace this link from an absolute one to a
relative.

website/content/docs/community-tools.mdx

@@ -19,7 +19,7 @@ vendors. These plugins are not officially tested nor officially maintained by
 HashiCorp, and are listed here in order to help users find them easily.
 
 To learn more about how to use community plugins, or how to build your own,
-check out the docs on [extending Packer](https://developer.hashicorp.com/packer/docs/plugins/install-plugins)
+check out the docs on [extending Packer](/packer/docs/plugins/install-plugins)
 
 If you have built a plugin and would like to add it to this community list,
 please make a pull request so that we can document your