Update the copyright header and use standard license file name

[oleg-nenashev]

subj

References

• TODO

Submitter checklist

• [ ] Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
• [ ] The PR request is well described and justified, including the body and the references
• [ ] The PR title represents the desired changelog entry
• [ ] The repository's code style is followed (see the contributing guide)
• [ ] Test coverage that demonstrates that the change works as expected
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