Ftr: Feature/application and service level router

[williamfeng323]

What this PR does:

1. Support multiple routers configuration in router_config.yml
2. Apply prioritization to routers
3. Enable service level routers
   Which issue(s) this PR fixes:

Fixes #596

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

After this change, the local router configuration file needs to follow below pattern to support multiple routing rules in local file configuration:

routerRules: 
  - scope: application
    key: mock-app1
    priority: 1
    force: true
    conditions :
      - "a => b"
      - "c => d"
  - scope: application
    key: mock-app2
    priority: 1
    force: true
    conditions :
      - "a => b"
      - "c => d"

the scope defines the rule's applicable range, 'application' | 'service'
the key defines the rule's applicable application name(for application scope) or the service key(for service scope, [{group}/]{service}[:{version}])

[codecov-commenter]

Codecov Report

Merging #662 into develop will increase coverage by 0.01%.
The diff coverage is 72.72%.

@@             Coverage Diff             @@
##           develop     #662      +/-   ##
===========================================
+ Coverage    63.80%   63.81%   +0.01%     
===========================================
  Files          236      236              
  Lines        12313    12329      +16     
===========================================
+ Hits          7856     7868      +12     
  Misses        3690     3690              
- Partials       767      771       +4     

Impacted Files	Coverage Δ
cluster/router/tag/router_rule.go	71.42% <ø> (ø)
common/yaml/yaml.go	86.66% <0.00%> (-13.34%)	⬇️
config/consumer_config.go	56.25% <ø> (ø)
config/provider_config.go	58.06% <ø> (ø)
config/router_config.go	70.37% <73.33%> (-4.63%)	⬇️
cluster/router/condition/file.go	91.30% <100.00%> (+0.60%)	⬆️
cluster/router/condition/router_rule.go	84.61% <100.00%> (ø)
cluster/cluster_impl/base_cluster_invoker.go	61.11% <0.00%> (-9.73%)	⬇️
cluster/cluster_impl/failback_cluster_invoker.go	78.02% <0.00%> (-2.20%)	⬇️
protocol/dubbo/client.go	67.87% <0.00%> (-1.22%)	⬇️
... and 2 more

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[zouyx]

What about those problems ? Do you need to change ?

[fangyincheng]

LGTM