Remove X-ConfigCat-UserAgent header

[z4kn4fein]

Describe the purpose of your pull request

This PR removes the X-ConfigCat-UserAgent request header. The SDK version is now a query param in the fetch URL.

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
0 Code Smells

No Coverage information
0.0% Duplication

[codecov[bot]]

Codecov Report

Merging #44 (6c8e6b6) into master (a755136) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 6c8e6b6 differs from pull request most recent head d67d6b4. Consider uploading reports for the commit d67d6b4 to get more accurate results

@@           Coverage Diff           @@
##           master      #44   +/-   ##
=======================================
  Coverage   78.57%   78.57%           
=======================================
  Files           3        3           
  Lines          56       56           
  Branches       10       10           
=======================================
  Hits           44       44           
  Misses         12       12           

Impacted Files	Coverage Δ
src/config-fetcher.ts	67.56% <ø> (ø)

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