Fix environment variables sharing

[NouemanKHAL]

What does this PR do?

• Changes the way she share env variables between our scripts, fixing issues with env variables format that are unsupported by dash or bash.
• Stops restarting the trace agent on CAPI metadata update.

Description of the Change

Instead of using export and source to export all env vars and import them.
We'll only export the env vars required by the datadog scripts using the function dd_export_env , and use safe_source to import them, which allows us to skip any failing ones if any instead of crashing the script.

Review checklist (to be filled by reviewers)

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