Ready for release 1.5.6

[cityiron]

What this PR does:

Add 1.5.6 change list to the file of CHANGE.md

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-io]

Codecov Report

Merging #1059 (c89648e) into 1.5 (968650f) will decrease coverage by 0.22%.
The diff coverage is 55.70%.

@@            Coverage Diff             @@
##              1.5    #1059      +/-   ##
==========================================
- Coverage   59.53%   59.31%   -0.23%     
==========================================
  Files         259      265       +6     
  Lines       12737    13092     +355     
==========================================
+ Hits         7583     7765     +182     
- Misses       4199     4349     +150     
- Partials      955      978      +23     

Impacted Files	Coverage Δ
cluster/cluster_impl/available_cluster.go	100.00% <ø> (ø)
cluster/router/healthcheck/factory.go	66.66% <0.00%> (ø)
cluster/router/tag/router_rule.go	89.47% <ø> (+12.20%)	⬆️
common/config/environment.go	51.72% <ø> (ø)
common/extension/config_post_processor.go	0.00% <0.00%> (ø)
common/extension/conn_checker.go	0.00% <0.00%> (ø)
common/extension/metadata_service.go	0.00% <0.00%> (ø)
common/proxy/proxy_factory/default.go	13.55% <0.00%> (+0.22%)	⬆️
config/base_config.go	64.02% <ø> (ø)
config_center/configurator/override.go	72.22% <0.00%> (ø)
... and 160 more

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