fix: set default selectedNetworkClientId to 'mainnet' if no matching with entry on network list

[salimtb]

Description

This PR implements a fix for Migration 60 to handle cases where selectedNetworkClientId does not match any entry within networkConfigurationsByChainId. If no corresponding networkClientId is found, the migration will now set selectedNetworkClientId to 'mainnet' by default.

Related issues

Fixes: #11657

Manual testing steps

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Screenshots/Recordings

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

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Commit hash: 217b7c7
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