Change some of the methods name into camle case instead of snake case

Signed-off-by: Ryan Liang <jiallian@amazon.com>

Author: RyanL1997

src/integrationTest/java/org/opensearch/security/http/OnBehalfOfJwtAuthenticationTest.java

@@ -79,7 +79,7 @@ public class OnBehalfOfJwtAuthenticationTest {
             )
         )
         .authc(AUTHC_HTTPBASIC_INTERNAL)
-        .onBehalfOf(new OnBehalfOfConfig().oboEnabled(oboEnabled).signing_key(signingKey).encryption_key(encryptionKey))
+        .onBehalfOf(new OnBehalfOfConfig().oboEnabled(oboEnabled).signingKey(signingKey).encryptionKey(encryptionKey))
         .build();
 
     @Test

src/integrationTest/java/org/opensearch/test/framework/OnBehalfOfConfig.java

@@ -27,12 +27,12 @@ public OnBehalfOfConfig oboEnabled(Boolean oboEnabled) {
         return this;
     }
 
-    public OnBehalfOfConfig signing_key(String signing_key) {
+    public OnBehalfOfConfig signingKey(String signing_key) {
         this.signing_key = signing_key;
         return this;
     }
 
-    public OnBehalfOfConfig encryption_key(String encryption_key) {
+    public OnBehalfOfConfig encryptionKey(String encryption_key) {
         this.encryption_key = encryption_key;
         return this;
     }