Adjust SDK to configcat-common v8.0

[adams85]

Describe the purpose of your pull request

Removes deprecated code.

Breaking changes:

• Removes the createClient, createClientWithAutoPoll, createClientWithManualPoll, createClientWithLazyLoad factory functions. Alternative: getClient.

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]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
5.5% Duplication

[sonarcloud[bot]]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
4.8% Duplication

[codecov[bot]]

Codecov Report

Patch coverage: 85.71% and project coverage change: -0.87 :warning:

Comparison is base (9dfc764) 91.13% compared to head (f90e456) 90.27%.

:exclamation: Current head f90e456 differs from pull request most recent head 913070f. Consider uploading reports for the commit 913070f to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #58 +/- ## ========================================== - Coverage 91.13% 90.27% -0.87% ========================================== Files 3 3 Lines 79 72 -7 Branches 9 9 ========================================== - Hits 72 65 -7 Misses 7 7 ``` | [Impacted Files](https://app.codecov.io/gh/configcat/node-sdk/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=configcat) | Coverage Δ | | |---|---|---| | [src/config-fetcher.ts](https://app.codecov.io/gh/configcat/node-sdk/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=configcat#diff-c3JjL2NvbmZpZy1mZXRjaGVyLnRz) | `88.00% <50.00%> (ø)` | | | [src/client.ts](https://app.codecov.io/gh/configcat/node-sdk/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=configcat#diff-c3JjL2NsaWVudC50cw==) | `95.23% <100.00%> (-1.20%)` | :arrow_down: |

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