feat: add BigPanda handler options

[alespour]

Required for all non-trivial PRs

• Rebased/mergable
• Tests pass
• CHANGELOG.md updated

This PR solves #2304.

1. adds the following options to the handler (per BigPanda Alert specification):

• host - corresponds to host alert payload parameter, ie. identifies "main object that caused the alert"
• attribute - option to add additional attribute(s) to the alert payload

The following template data are available in host and attribute value expressions: ID, Message, Level, Time, Duration, Details, Name, TaskName, Group, Tags, Fields.

2. tags and fields are added to the payload as additional attributes. A new handler configuration option auto-attributes has been added to control this behavior. The value can be either "tags", "fields" or both these keywords (comma-separated). For backward compatibility with previous version, default value is "tags,fields".

Example:

stream
  |from()
    .database('telegraf')
    .measurement('cpu')
    .groupBy('host')
    .where(lambda: "cpu" == 'cpu-total')
  |eval(lambda: 100.0 - "usage_idle").as('total_used')
  |window().period(10s).every(10s)
  |mean('total_used').as('total_used')
  |alert()
    .id('cpu_usage_check')
    .message('Hey {{ index .Tags "host"}} / {{ .ID }}: is high!')
    .details('https://example.com/dashboard/{{ index .Tags "host"}}')
    .info(lambda: "total_used" > 70)
    .warn(lambda: "total_used" > 80)
    .crit(lambda: "total_used" > 90)
    .bigPanda()
      .host('{{ .Tags.host }}')
      .attribute('monitor_link', 'http://example.com/monitor?node={{ .Tags.host }}')
      .attribute('x_total_used', '{{ .Fields.total_used }}')

Payload:

{
  "app_key": "8f5795cada387b9f310f41fc369c88e4",
  "check": "cpu_usage_check",
  "description": "Hey localhost / cpu_usage_check: is high!",
  "details": "https://example.com/dashboard/server-1",
  "host": "server-1",
  "monitor_link": "http://example.com/monitor?node=server-1",
  "status": "critical",
  "task": "cpu_usage_check:cpu",
  "timestamp": 1633010510,
  "x_total_used": "92.53376688320374",
}

[docmerlin]

@alespour is this ready?

[alespour]

@docmerlin Yes. Thank you.