Implement the remaining use cases listed here https://docs.google.com/document/d/1nLLUsEC3cc_toAIeqJsw25FSJ-NqdW6_JxprvXVScn4/edit?tab=t.0 based on work in NETOBSERV-2326

It consists in 2 alerts:

• ExternalEgressHighTrend, triggered when the volume of external egress is increasing
• ExternalIngressHighTrend, triggered when the volume of external ingress is increasing

For both of them, thresholds are:

• Per node, over 200% of increase => warning
• Per namespace, over 100% of increase => info
• Per namespace, over 500% of increase => warning

Note that my initial design planned a "CrossAZ" alert, but I didn't implement it because after some tests I don't find it relevant, I don't think it's an easy thing to alert on, as there can always be large cross-AZ traffic for very good reasons, it's hard to distunguish good vs bad reasons.