output_extract for external circonus_checks should support regular expressions

[mostfunkyduck]

Terraform Version

Terraform v0.12.13

• provider.circonus v0.8.0

Affected Resource(s)

• circonus_check

Terraform Configuration Files

resource "circonus_check" "ieh_metrics" {
    active               = true
    metric_limit         = 0 
    name                 = "example"
    period               = "20s"
    tags                 = []
    target               = "blah"
    timeout              = "10s"
    type                 = "external"

    collector {
        id = "/broker/370"
    }   

    external {
        arg1           = "%[target]"
        command        = "/path/to/file.sh"
        output_extract = "(?<key>\\S+) (?<type>[a-zA-Z]) (?<value>\\S+)"
    }
  metrics...
}

Expected Behavior

This should create an external check.
The circonus documentation supports arbitrary regular expressions in output_extract https://docs.circonus.com/circonus/checks/check-types/external/#using-the-output-extract

Actual Behavior

What actually happened?
The code limits the output to the phrases "JSON" or "NAGIOS"
https://github.com/terraform-providers/terraform-provider-circonus/blob/57d100d890ac65522b947296bbfacdca05ef55d6/circonus/resource_circonus_check_external.go#L32

This results in the following error:
Error: Invalid output_extract specified ("(?<key>\\S+) (?<type>[a-zA-Z]) (?<value>\\S+)"): regexp failed to match string

Steps to Reproduce

Attempt to create an external check that uses a value besides 'JSON' or 'NAGIOS' for its output_extract

[maier]

Fixed in PR #49, v0.9.0 has been released.