Release note for glance config opts.

Adding a release note stating the work on improving configuration
options of Glance for this release.
Some of the configuration options in Glance were set
with a ``min``, preventing them to accept negative integers like
in the previous release. This release note will give operators a
heads up on this.

This note is copied and modifed for glance from
I8db8764f84c92e987a774ce3650beb53d9635905
which was originally done for glance_store

Co-Authored-By: Dharini Chandrasekar <dharini.chandrasekar@intel.com>

Change-Id: I1afaa7206bd964409c343abcc385eff9dbf6b2ed

releasenotes/notes/improved-config-options-221c58a8c37602ba.yaml

@@ -0,0 +1,29 @@
+---
+prelude: >
+    Improved configuration options for glance. Please
+    refer to the ``other`` section for more information.
+
+other:
+  - The glance configuration options have been
+    improved with detailed help texts, defaults for
+    sample configuration files, explicit choices
+    of values for operators to choose from, and a
+    strict range defined with ``min`` and ``max``
+    boundaries.
+
+    It must be noted that the configuration options
+    that take integer values now have a strict range defined
+    with "min" and/or "max" boundaries where appropriate. This
+    renders the configuration options incapable of taking certain
+    values that may have been accepted before but were actually
+    invalid. For example, configuration options specifying counts,
+    where a negative value was undefined, would have still accepted
+    the supplied negative value. Such options will no longer accept
+    negative values. However, options where a negative value was
+    previously defined (for example, -1 to mean unlimited) will
+    remain unaffected by this change.
+
+    Values that do not comply with the appropriate restrictions
+    will prevent the service from starting. The logs will contain
+    a message indicating the problematic configuration option and
+    the reason why the supplied value has been rejected.