public void addRule(String serviceName, String endpointGroupName, String ruleRegex) {
        final StringFormatGroup formatGroup = rules.computeIfAbsent(serviceName, name -> new StringFormatGroup());
        formatGroup.addRule(endpointGroupName, ruleRegex);
    }
Add a new rule to the context.

@param serviceName       of the new rule
@param endpointGroupName represents the logic endpoint name.
@param ruleRegex         match the endpoints which should be in the group name.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/config/group/EndpointGroupingRule.java