Catch exceptions thrown by Slack SDK

[jkehres]

I would agree with this issue:

slackapi/node-slack-sdk#775

Error handling is not intuitive for the Slack SDK. The result object returned by an API call has an ok property, which indicates the API will never reject/throw and you need to check the result to determine the success. However, in practice the SDK will reject/throw. We are not currently handling this in the code. This is particularly bad in the stream lambda since we could stuck trying to process the same record forever when we hit a Slack API error that is permanent.

[jkehres]

Here is an example error object thrown by the SDK:

{
    "errorType": "Error",
    "errorMessage": "An API error occurred: channel_not_found",
    "code": "slack_webapi_platform_error",
    "data": {
        "ok": false,
        "error": "channel_not_found",
        "response_metadata": {
            "scopes": [
                "identify",
                "bot:basic"
            ],
            "acceptedScopes": [
                "chat:write:bot",
                "post"
            ]
        }
    },
    "stack": [
        "Error: An API error occurred: channel_not_found",
        "    at Object.platformErrorFromResult (/var/task/node_modules/@slack/web-api/dist/errors.js:50:33)",
        "    at WebClient.apiCall (/var/task/node_modules/@slack/web-api/dist/WebClient.js:423:28)",
        "    at process._tickCallback (internal/process/next_tick.js:68:7)"
    ]
}