Add EventBridge infrastructure

[gregtyler]

Includes:

• Event bus in LPA Store account
• Cross-account rule to send all locally-sourced events to the Sirius event bus
• Dead letter-queue to catch events that couldn't be sent

Fixes VEGA-2333 #minor

[gregtyler]

Tested in a popup environment with the code:

l.eb.PutEvents(&eventbridge.PutEventsInput{
	Entries: []*eventbridge.PutEventsRequestEntry{
		{
			EventBusName: aws.String(os.Getenv("EVENT_BUS_NAME")),
			DetailType:   aws.String("test"),
			Source:       aws.String("opg.poas.lpastore"),
			Detail:       aws.String("{\"ok\": true}"),
		},
	},
})