Feat: need support cron hpa

[StevenLeiZhang]

Signed-off-by: StevenLeiZhang zhangleiic@163.com

fix:#573

Description of your changes

build one addon based on https://github.com/AliyunContainerService/kubernetes-cronhpa-controller

After addon installed, one new Trait is exposed, which is named "cronhpa". User could use it to set cronhpa for Component.

How has this code been tested?

test it locally.

1. install it

cd experimental/addons/cronhpa
vale addon enable ./

2. wait for it is up
   3.run test Application

cd examples/cronhpa
kubectl apply -f cronhpa-sample.yaml

4. check the pod amount of helloworld Application.
   It will scale up and down every 30s.

Checklist

I have:

• Title of the PR starts with type (e.g. [Addon] , [example] or [Doc]).
• Updated/Added any relevant documentation and examples.
• New addon should be put in experimental.
• Update addon should modify the version in metadata.yaml to generate a new version.

Verified Addon promotion rules

If this pr wants to promote an experimental addon to verified, you must check whether meet these conditions too:

• This addon must be tested by addon's e2e-test to guarantee this addon can be enabled successfully.
• This addon must have some basic but necessary information.
  • An accessible icon url and source url defined in addon's metadata.yaml.
  • A detail introduction include a basic example about how to use and what's the benefit of this addon in README.md.
  • Also provide an introduction in KubeVela documentation.
  • It's more likely to be accepted if useful examples provided in example dir.

[wangyikewxgm]

Cool works!

[wangyikewxgm]

LGTM

[wonderflow]

Please add applyonce policy in example

[StevenLeiZhang]

Please add applyonce policy in example

Done