[Proposal] events service for pouchd

[HusterWan]

Ⅰ. Issue Description

When creating or deleting a container, pouchd will operate many objects, like container, snapshot, volume, network and so on. If can recording those actions of all objects, we can use those records for monitoring a container's all actions in it's life circle.

So we need an events service to record all actions of containers, suppose it at least has two common functions:

• Publish: log the action when a event occurs
• Subscribe : subscribe all events on the hosts, we also should support filter to filter some events that we do not care about.

I will finish this function, but in order to relieve the pressure of code review, i will break the whole service into four parts:

• events package: this will only contains events service core code
• api bridge: finish the api for event
• collect events from containerd: there are some events not produced by pouchd but containerd, like OOM, container exited abnormally and so on, we also should collect those events and publish them to events service
• event cli: finish cli tool for event

Ⅱ. Describe what happened

Ⅲ. Describe what you expected to happen

Ⅳ. How to reproduce it (as minimally and precisely as possible)

Ⅴ. Anything else we need to know?

Ⅵ. Environment:

• pouch version (use pouch version):
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others: