Document setGenerationTime removal and add back the method #16860

Description:

fix https://github.com/matomo-org/matomo/issues/16853

created https://github.com/matomo-org/matomo/issues/16859 as a follow up

for now it's just important to have this method again in the JS tracker as it otherwise can cause errors

Review

• [ ] Functional review done
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done see checklist
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

build js