Consistent config caching

[adams85]

Describe the purpose of your pull request

Makes the changes necessary for having a generalized config cache interface and implementation across SDKs.

Breaking changes:

• Changes the type of the cached value from ProjectConfig to string in IConfigCatCache.
• Changes the type of the NewConfig property from ProjectConfig to IConfig in ConfigChangedEventArgs.
• Removes the ProjectConfig class from the public API.
• Changes the type of the MatchedEvaluationRule to ITargetingRule and MatchedEvaluationPercentageRule to IPercentageOption in EvaluationDetails.
• Removes the RolloutRule and RolloutPercentageItem classes from the public API.
• Changes the algorithm used to generate the config cache key and the format of the cache payload.

Also proposes an improvement to HttpConfigFetcher to ensure that only a single HTTP request can be in progress at a time, regardless of the fetch operation being initiated from sync or async code.

Related issues (only if applicable)

Provide links to issues relating to this pull request

Requirement checklist (only if applicable)

• [x] I have covered the applied changes with automated tests.
• [x] I have executed the full automated test set against my changes.
• [x] I have validated my changes against all supported platform versions.
• [x] I have read and accepted the contribution agreement.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

88.7% Coverage
0.0% Duplication