docs(proposals): use glob toctree to prevent merge conflicts

Replace the hand-maintained file list in docs/proposals/index.rst with
Sphinx's :glob: directive. This eliminates recurring merge conflicts
when multiple proposal PRs are open simultaneously, as new proposals
no longer need to modify the index file.

Closes: #1108
Signed-off-by: Shanmukh Pawan <smoparth@redhat.com>

Author: smoparth

docs/proposals/index.rst

@@ -3,8 +3,6 @@ Fromager Enhancement Proposals
 
 .. toctree::
    :maxdepth: 1
+   :glob:
 
-   iterative-bootstrap
-   new-patcher-config
-   new-resolver-config
-   release-cooldown
+   *