Minor improvements

[adams85]

Describe the purpose of your pull request

Besides some minor perf/code quality improvements, makes changes to the implementation of LocalStorageCache:

• Upon client initialization test for the availability of the local storage and use LocalStorageCache only if it's available. Otherwise, use the default (in-memory) cache implementation.
• Don't swallow exceptions which are thrown in the LocalStorageCache.get/set methods so the outer exception handlers can catch and log them.

Also:

• Send etag as a query string parameter when running in browser because browsers don't send it automatically in every case.
• Update to configcat-common v9.1.0.

Related issues (only if applicable)

• https://trello.com/c/X2E439F9
• https://trello.com/c/GNdjdMxP

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.

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (b3dd995) 85.41% compared to head (1e83801) 85.93%.

Files	Patch %	Lines
src/ConfigFetcher.ts	60.00%	1 Missing and 1 partial :warning:
src/Cache.ts	96.42%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #78 +/- ## ========================================== + Coverage 85.41% 85.93% +0.52% ========================================== Files 3 3 Lines 48 64 +16 Branches 8 12 +4 ========================================== + Hits 41 55 +14 - Misses 4 6 +2 Partials 3 3 ```

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[sonarcloud[bot]]

Quality Gate passed

The SonarCloud Quality Gate passed, but some issues were introduced.

2 New issues
0 Security Hotspots
No data about Coverage
0.9% Duplication on New Code

See analysis details on SonarCloud