Thread Safe mode (ZTS) support

[nmolham-godaddy]

Is your feature request related to a problem? Please describe. Testing the agent with FrankenPHP server which runs PHP in ZTS mode yields the extensions unable to load:

INFO  [elastic_apm_loader][PID: 136][TID: 148] Thread Safe mode (ZTS) is not supported by Elastic APM Agent

Describe the solution you'd like Adding support for Thread Safe mode (ZTS)

Describe alternatives you've considered The only alternative I can think of is building a custom FrankenPHP version with APM agent extension compiled In, which is not viable due to:

• Requires complex multi-stage Docker build
• Significant build time
• High maintenance burden for updates
• Build complexity makes debugging difficult

Thanks for the awesome work your team is doing