[FEATURE] Configurable message format alert

[dwisiswant0]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Describe the solution you'd like
Example:

  slack:
    webhook: "https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX"
    token: "xoxo-...."
    color: "#ffd21a"
    channel: "G30SPKI"
    # Browse available fields at https://pkg.go.dev/github.com/slack-go/slack#Attachment
    format:
      - Title: "Request"
        Text: "{{ .request_method }} {{ .request_uri }} {{ .request_protocol }}"

      - Fields:
        - Title: "Date"
          Value: "{{ .time_local }}"
          Short: true

        - Title: "IP Address"
          Value: "{{ .remote_addr }}"
          Short: true

        - Title: "User-Agent"
          Value: "{{ .http_user_agent }}"
          Short: true

        - Title: "Referer"
          Value: "{{ .http_referer }}"
          Short: true

        - Title: "Status code"
          Value: "{{ .status }}"
          Short: true

        - Title: "Bytes sent"
          Value: "{{ .body_bytes_sent }}"
          Short: true

  mattermost:
    webhook: "http://HOST/hooks/XXXXX-KEY-XXXXX"
    color: "#ffd21a"
    # The message format for Slack is compatible with Mattermost, so it's basically the same.
    format:
      - Title: "Request"
        Text: "{{ .request_method }} {{ .request_uri }} {{ .request_protocol }}"

      - Fields:
        - Title: "Date"
          Value: "{{ .time_local }}"
          Short: true

        - Title: "IP Address"
          Value: "{{ .remote_addr }}"
          Short: true

        - Title: "User-Agent"
          Value: "{{ .http_user_agent }}"
          Short: true

        - Title: "Referer"
          Value: "{{ .http_referer }}"
          Short: true

        - Title: "Status code"
          Value: "{{ .status }}"
          Short: true

        - Title: "Bytes sent"
          Value: "{{ .body_bytes_sent }}"
          Short: true

  telegram:
    token: "123456:ABC-DEF1234...-..."
    chat_id: "-111000"
    format: |
      Request: `{{ .request_method }} {{ .request_uri }} {{ .request_protocol }}`
      Date: `{{ .time_local }}`
      IP Address: `{{ .remote_addr }}`
      User\-Agent: `{{ .http_user_agent }}`
      Referrer: `{{ .http_referer }}`
      Status code: `{{ .status }}`
      Bytes sent: `{{ .body_bytes_sent }}`

  discord:
    webhook: "https://discord.com/api/webhooks/0000000000/XXXXX"
    token: "NkWkawkawkawkawka.X0xo.n-kmZwA8aWAA"
    color: "16312092"
    channel: "700000000000000..."
    format:
      Fields:
        - Name: "Request"
          Value: "{{ .request_method }} {{ .request_uri }} {{ .request_protocol }}"

        - Name: "Date"
          Value: "{{ .time_local }}"
          Inline: true

        - Name: "IP Address"
          Value: "{{ .remote_addr }}"
          Inline: true

        - Name: "User-Agent"
          Value: "{{ .http_user_agent }}"
          Inline: true

        - Name: "Referer"
          Value: "{{ .http_referer }}"
          Inline: true

        - Name: "Status code"
          Value: "{{ .status }}"
          Inline: true

        - Name: "Bytes sent"
          Value: "{{ .body_bytes_sent }}"
          Inline: true

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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