Describe the purpose of your pull request

Prepare v9.4.0 release, along with the following minor improvements:

• Make redirect logic consistent with other SDKs (and simplify DefaultConfigFetcher at the same time)
• Fix minor bug in ConfigCatClientSnapshot.GetValue/GetValueDetails. (Report correct error codes.)
• Include the SDK Key in log message of error 1100 ("Your SDK Key seems to be wrong...")
• Mask SDK Key (keep only the last 6 characters visible) when writing it to the log.

Related issues (only if applicable)

https://trello.com/c/pcqhSFw8

How to test? (only if applicable)

n/a

Security (only if applicable)

n/a

Requirement checklist (only if applicable)

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