修改ConfigServer启动类，提供配置功能，开启或关闭EurekaServer功能

[linzhiqiang0514]

根据属性配置，
1、开启或者关闭eurekaServer，默认开启
2、开启或者关闭eurekaClient，默认关闭。

[nobodyiam]

禁用eureka之后服务发现如何实现？

[linzhiqiang0514]

禁用eureka之后服务发现如何实现？

自行搭建eureka。
有些公司的项目是已经有eureka的，完全没有必要用这个自带的，而且，本身设置文档里，也支持使用外部的eureka。

[codecov-io]

Codecov Report

Merging #2478 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #2478      +/-   ##
============================================
- Coverage     50.21%   50.21%   -0.01%     
- Complexity     2044     2045       +1     
============================================
  Files           408      410       +2     
  Lines         12541    12543       +2     
  Branches       1281     1281              
============================================
+ Hits           6298     6299       +1     
  Misses         5798     5798              
- Partials        445      446       +1

Impacted Files	Coverage Δ	Complexity Δ
...apollo/configservice/ConfigServiceApplication.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...nfigservice/ConfigServerEurekaServerConfigure.java	100% <100%> (ø)	1 <1> (?)
...nfigservice/ConfigServerEurekaClientConfigure.java	100% <100%> (ø)	1 <1> (?)
...ervice/service/ReleaseMessageServiceWithCache.java	85.88% <0%> (-1.18%)	24% <0%> (-1%)

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[coveralls]

Coverage increased (+0.007%) to 53.775% when pulling 4e9c09d on linzhiqiang0514:master into 2d02cbf on ctripcorp:master.

[nobodyiam]

LGTM