fix: only send 'activation_method' to APM server >=8.7.1

[trentm]

This works around an issue in APM server 8.7.0 which had problems
receiving metadata with activation_method.

Closes: #3230

[ghost]

💔 Build Failed

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• Start Time: 2023-03-31T00:22:12.641+0000

• Duration: 18 min 16 sec

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Windows Batch Script

• Took 0 min 13 sec . View more details here
• Description: node test/test.js

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• Description: hudson.AbortException: script returned exit code 1

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[trentm]

Waiting for a 11.3.1 version of the http-client, pending spec discussions at elastic/apm#783.

[trentm]

Waiting for a 11.3.1 version of the http-client

Done in elastic/apm-nodejs-http-client#198