Add option for detecting changes to flag overrides

[adams85]

Describe the purpose of your pull request

Adds an optional parameter named watchChanges to createFlagOverridesFromMap which controls whether the client should detect changes to the flag override map after client initialization.

Related issues (only if applicable)

https://trello.com/c/9jqzNyAI/381-konzisztencian%C3%B6vel%C5%91-improvementek

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]]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (8e2e8e9) 85.93% compared to head (477348b) 86.88%.

Files	Patch %	Lines
src/index.ts	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #79 +/- ## ========================================== + Coverage 85.93% 86.88% +0.94% ========================================== Files 3 3 Lines 64 61 -3 Branches 12 12 ========================================== - Hits 55 53 -2 + Misses 6 5 -1 Partials 3 3 ```

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