agent: define new flags to control Cilium's datapath events notifications

[EricMountain]

Cherry-pick of cilium#30063 (430ccca).

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This commit introduces three new configuration flags for the Cilium agent, allowing users to choose the bpf event types they want to expose to Cilium monitor and Hubble.

• --bpf-events-drop-enabled Expose 'drop' events for Cilium monitor and/or Hubble (default true)
• --bpf-events-policy-verdict-enabled Expose 'policy verdict' events for Cilium monitor and/or Hubble (default true)
• --bpf-events-trace-enabled Expose 'trace' events for Cilium monitor and/or Hubble (default true)

The default values for these flags remain set to true, not changing the current behaviour.

In our case, we found particularly useful to disable the TraceNotification in order to reduce the CPU overhead on some of our nodes when Hubble is enabled as we were mostly interested into dropped packets.

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Fixes: #issue-number

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