bug/OTF-4041: dd support for non-JWT OAuth2 tokens in OAuth2Util

- Added IllegalArgumentException to catch block in expiresAtMillis method
- Enables compatibility with BigLake API which uses opaque OAuth2 access tokens
- Maintains backward compatibility with existing JWT-based token systems
- Returns null for non-JWT tokens, allowing expiration fallback to properties

Author: Ashok Vengala

core/src/main/java/org/apache/iceberg/rest/auth/OAuth2Util.java

@@ -441,7 +441,7 @@ static Long expiresAtMillis(String token) {
     JsonNode node;
     try {
       node = JsonUtil.mapper().readTree(Base64.getUrlDecoder().decode(parts.get(1)));
-    } catch (IOException e) {
+    } catch (IOException | IllegalArgumentException e) {
       return null;
     }