Telegraf helm chart output tagpass and tagdrop should not generate double brackets

[peterbaumert]

Same issue like in #375 just this time for outputs.

values.yaml:

  outputs:
    - basicstats:
        period: "30s"
        drop_original: true
        stats:
          - "sum"
        taginclude:
          - "counter"
          - "sql_instance"
        tagpass: 
          counter:
            - "Blocked tasks"
            - "CPU usage %"
            - "Used memory (KB)"

expected output:

    [[outputs.basicstats]]
      drop_original = true
      period = "30s"
      stats = [
        "sum"
      ]
      taginclude = [
        "counter",
        "sql_instance"
      ]
      [outputs.basicstats.tagpass]
        counter = [
                  "Blocked tasks",
                  "CPU usage %",
                  "Used memory (KB)"
        ]

actual output:

    [[outputs.basicstats]]
      drop_original = true
      period = "30s"
      stats = [
        "sum"
      ]
      taginclude = [
        "counter",
        "sql_instance"
      ]
      [[outputs.basicstats.tagpass]]
        counter = [
                  "Blocked tasks",
                  "CPU usage %",
                  "Used memory (KB)"
        ]