Alert Email Template Refine

[suiguoxin]

• add kill user job alert template alert handler stop-job notice not clear to end user #5021
• add troubleshooting link in general email template
• redefine actions schema in customized-receivers to facilitate parameters passing

Email Examples:
User:

Admin:

[coveralls]

Coverage remained the same at 34.103% when pulling a4636e0 on suiguoxin:template-refine into da3abef on microsoft:master.

[Binyang2014]

Just wondering if we can put all ejs into separate folder, such as template folder and not build them into docker image (We can make them as a configmap and mount into container). So if customer want to change/add some templates, they just need to change some config.