feature: Support to register custom condition types

[rameshmalla]

Is your feature request related to a problem? Please describe.
By default, baigan supports the following conditions which can be used in the configurations.

• Equals
• In
• EndsWith

To introduce a custom conditions, such as for gradual rollout of a feature, it is required to make changes directly to the baigan source code. As a result, impacting extension capability of baigan.

Describe the solution you'd like
The proposal is to make use of jackson polymorphic deserialization, by which baigan could provide the capability to register condition types directly to the objectmapper. This would allow the client to define their own custom condition types and register the relevant types while initializing configuration repository

Example

class StartsWith extends ConditionType{

    private final String startsWithValue;

    @JsonCreator
    public StartsWith(@JsonProperty("startsWithValue") final String startsWithValue) {
        this.startsWithValue = startsWithValue;
    }
    @Override
    public boolean eval(@Nullable final String paramValue) {
        return StringUtils.startsWithIgnoreCase(paramValue, startsWithValue);
    }
}

class Application{

        @Bean
        ConfigurationRepository configurationRepository(RepositoryFactory repositoryFactory) {

            final ObjectMapper objectMapper = new ObjectMapper().configure(FAIL_ON_UNKNOWN_PROPERTIES, false);

            return repositoryFactory.fileSystemConfigurationRepository()
                    .fileName(FileSystemConfigurationContextProviderEnd2EndTest.class.getClassLoader().getResource("test-config.json").getPath())
                    .refreshInterval(CONFIG_REFRESH_INTERVAL)
                    .objectMapper(objectMapper)
                    .conditions(StartsWith.class) // register new condition
                    .build();
        }

}



//somewhere in baigan we can register these condition types.
....
 public void registerConditions(final List<Class<? extends ConditionType>> conditionTypes) {
        registerDefaultConditions();
        conditionTypes.forEach(this.objectMapper::registerSubtypes);
    }

    private void registerDefaultConditions(){
        DEFAULT_CONDITION_TYPES.forEach(this.objectMapper::registerSubtypes);
    }