Fix the issue of case sensitivity when matching keys with cache enabled

[klboke]

What's the purpose of this PR

Fix the issue of case sensitivity when matching keys with cache enabled

• Add a configuration config-service.cache.key.ignore-case to control whether the cache key is case-sensitive.

Which issue(s) this PR fixes:

Fixes #3529

[codecov]

Codecov Report

Merging #4820 (c274197) into master (2800a00) will decrease coverage by 0.07%.
The diff coverage is 83.33%.

@@             Coverage Diff              @@
##             master    #4820      +/-   ##
============================================
- Coverage     48.43%   48.36%   -0.07%     
- Complexity     1721     1722       +1     
============================================
  Files           346      346              
  Lines         10819    10827       +8     
  Branches       1076     1078       +2     
============================================
- Hits           5240     5237       -3     
- Misses         5257     5268      +11     
  Partials        322      322              

Impacted Files	Coverage Δ
.../configservice/ConfigServiceAutoConfiguration.java	91.66% <0.00%> (ø)
...service/service/config/ConfigServiceWithCache.java	78.66% <87.50%> (+2.19%)	⬆️
...m/ctrip/framework/apollo/biz/config/BizConfig.java	49.29% <100.00%> (+0.72%)	⬆️

... and 2 files with indirect coverage changes

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[nobodyiam]

This attempt is commendable, but a problem may arise if the database is set to be case-sensitive. In such a scenario, the cache loader would fail to fetch data from the database, since the appid, cluster, and namespace have all been converted to lowercase.

[klboke]

but a problem may arise if the database is set to be case-sensitive. In such a scenario, the cache loader would fail to fetch data from the database, since the appid, cluster, and namespace have all been converted to lowercase.

There is indeed such a situation, and this PR also considers it. It is currently not enabled by default, and needs to be enabled through a configuration switch. This has also been prominently explained in the documentation.

[nobodyiam]

LGTM