Queries for custom dynamic filters

[DifferentialOrange]

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Now user may set the following filters

filters: {
  job: ['=~', '$job'],
  alias: ['=~', '$alias'],
}

and get the dashboard with job, alias dynamic variables and filters. User may also add

mylabel: ['=~'. '$myval']

but they will need to add a query for variable $myvar manually later. We can make their lives easier by

• supporting writing custom variable queries in YAML config,
• providing a default query for dynamic filter if there is no user one, similar to job and alias.