feat: migrate 'api key' storage data to 'instance name' storage

[falconandy]

Summary

Migrate 'api key' storage data to 'instance name' storage. Implementation and test are similar to Amplitude-Swift (https://github.com/amplitude/Amplitude-Swift/pull/63)

Checklist

• [x] Does your PR title have the correct title format?
• Does your PR have a breaking change?: No

[github-actions[bot]]

:tada: This PR is included in version 1.11.0 :tada:

The release is available on:

• GitHub release
• v1.11.0

Your semantic-release bot :package::rocket: