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feat:import and export configs

version to 1.3.0-SNAPSHOT

refactoring namespace service a little.

1.2.0

add missing env and namespace alert

refresh namespace when doing lazy load

do lazy load if page contains too many namespaces(>10)

hidden namespace's body when namespace's size bigger than 2

allow users to create missing appnamespaces and private namespaces

Enhance open api capabilities

1. Add get single item interface
2. Allow passing the appendNamespacePrefix flag when creating public namespaces

Use DefaultHttpFirewall instead of default StrictHttpFirewall for apollo meta service to avoid 'The request was rejected because the URL was not normalized' issue.

使用DefaultHttpFirewall替换spring security默认的StrictHttpFirewall，用于解决客户端配置meta url时加上/，抛The request was rejected because the URL was not normalized.异常的问题

Fixes gray release issue #1677

use weak reference to hold bean objects so that they could be garbage collected