feat: allow claimModifier to replace old value (configurable)

perun-oidc-server/src/main/java/cz/muni/ics/oidc/server/claims/ClaimModifier.java

 package cz.muni.ics.oidc.server.claims;
 
+import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
 
 /**
@@ -15,9 +16,13 @@ public abstract class ClaimModifier {
 	private final String claimName;
 	private final String modifierName;
 
+	@Getter
+	private final boolean replaceOldValue;
+
 	public ClaimModifier(ClaimModifierInitContext ctx) {
 		this.claimName = ctx.getClaimName();
 		this.modifierName = ctx.getModifierName();
+		this.replaceOldValue = ctx.isReplaceOldValue();
 		log.debug("{} - claim modifier initialized", ctx.getClaimName());
 	}