Update master for stable/2025.1

Add file to the reno documentation build to show release notes for
stable/2025.1.

Use pbr instruction to increment the minor version number
automatically so that master versions are higher than the versions on
stable/2025.1.

Sem-Ver: feature
Change-Id: I742fad68e041d146a3b52ff9b7bad986cee43c2b

releasenotes/source/2025.1.rst

@@ -0,0 +1,6 @@
+===========================
+2025.1 Series Release Notes
+===========================
+
+.. release-notes::
+   :branch: stable/2025.1

releasenotes/source/index.rst

@@ -6,6 +6,7 @@
    :maxdepth: 1
 
    current
+   2025.1
    2024.2
    2024.1
    2023.2