Config service cache and namespace name normalization

[nobodyiam]

1. Enable config cache to improve config service performance, just set config-service.cache.enabled to true in ServerConfig
2. Normalize the namespace name in case the one provided has character case issue

[coveralls]

Coverage increased (+0.7%) to 50.871% when pulling 699009f on nobodyiam:configservice-cache-merge into f68cb45 on ctripcorp:master.

[codecov-io]

Codecov Report

Merging #719 into master will increase coverage by 0.63%.
The diff coverage is 73.33%.

@@             Coverage Diff              @@
##             master     #719      +/-   ##
============================================
+ Coverage     46.73%   47.36%   +0.63%     
- Complexity     1482     1535      +53     
============================================
  Files           341      347       +6     
  Lines          9392     9583     +191     
  Branches        928      949      +21     
============================================
+ Hits           4389     4539     +150     
- Misses         4679     4708      +29     
- Partials        324      336      +12

Impacted Files	Coverage Δ	Complexity Δ
...llo/adminservice/controller/ReleaseController.java	21.42% <ø> (ø)	3 <0> (ø)	⬇️
...nservice/controller/NamespaceBranchController.java	2.5% <ø> (ø)	1 <0> (ø)	⬇️
...nfigservice/controller/NotificationController.java	89.09% <ø> (ø)	12 <0> (ø)	⬇️
...work/apollo/core/dto/ApolloConfigNotification.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...rk/apollo/core/dto/ApolloNotificationMessages.java	0% <0%> (ø)	0 <0> (?)
...m/ctrip/framework/apollo/biz/config/BizConfig.java	25% <10.52%> (-1.83%)	7 <1> (ø)
...ework/apollo/internals/RemoteConfigRepository.java	87.82% <100%> (+1.06%)	22 <0> (+2)	⬆️
...nfigservice/wrapper/CaseInsensitiveMapWrapper.java	100% <100%> (ø)	4 <4> (?)
...ework/apollo/configservice/util/NamespaceUtil.java	100% <100%> (ø)	6 <3> (+3)	⬆️
...framework/apollo/biz/service/NamespaceService.java	62.73% <100%> (+0.46%)	32 <0> (ø)	⬇️
... and 23 more

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