add minimal server version for activation_method

[SylvainJuge]

APM Server version 8.7.0 contains a bug that prevents agents from sending metrics when the service.agent.activation_method is present in metadata.

In addition of some error messages in APM server logs, the most visible impact is the lack of metrics in Kibana UI for the service.

Related APM Server issue: https://github.com/elastic/apm-server/issues/10551

This should be fixed for 8.7.1 with https://github.com/elastic/apm-server/pull/10552

As a way to mitigate extra support issues, making the agents only send this field for newer apm-server versions (8.7.1 and later) is required.

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• May the instrumentation collect sensitive information, such as secrets or PII (ex. in headers)?
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• [x] Create PR as draft
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• [ ] Approved by at least 2 agents + PM (if relevant)
• [ ] Merge after 7 days passed without objections \ To auto-merge the PR, add /schedule YYYY-MM-DD to the PR description.
• [ ] Create implementation issues through the meta issue template (this will automate issue creation for individual agents)
• [x] If this spec adds a new dynamic config option, add it to central config. N/A

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#### Build stats * Start Time: 2023-03-30T12:58:53.025+0000 * Duration: 3 min 1 sec