Use valid identifiers for x-enum-varnames

openapi-generator (which is the only generator I am aware of which
supports x-enum-varnames) uses x-enum-varnames as identifiers verbatim.
Therefore, they must be valid identifiers (in all languages).
Unfortunately, whatever capitalization convention we use will look weird
in some languages.  Choose a common one for now.

See OpenAPITools/openapi-generator#3246 for discussion.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

openapi.yaml

@@ -2502,10 +2502,13 @@ components:
       - 0
       - 1
       - 2
+      # Note: x-enum-varnames used as identifiers verbatim by openapi-generator.
+      # Choice of identifier casing convention is necessarily arbitrary.
+      # https://github.com/OpenAPITools/openapi-generator/issues/3246
       x-enum-varnames:
-      - Any
-      - Only Selected
-      - All Except Selected
+      - ANY
+      - ONLY_SELECTED
+      - ALL_EXCEPT_SELECTED
       x-enum-descriptions:
       - Any project can be deployed to the environment.
       - Only selected projects can be deployed to the environment.