[TECH DEBT] slackboltengine is using an expiring api

Description of the tech debt to be addressed, include links and screenshots

Slackengine (bolt) is using an api thats being removed
https://docs.slack.dev/changelog/2024-04-a-better-way-to-upload-files-is-here-to-stay/

I received this message from slack recently on an api key thats only ever been used by the new slackengine using bolt

👋  Action required: Important notice about the files.upload API 

You are receiving this message because we have detected that your NetworkSaltSlackEngine app has recently made a call to the files.upload API.

We want to remind you that on November 12, 2025, support for this API will be discontinued. Please prepare for this change by moving away from using files.upload and instead use the combination of files.getUploadURLExternal and files.completeUploadExternal. More information on how to use these two APIs together can be found on our Working with files documentation. You can also leverage Slack's SDKs to help you transition to this new way of uploading files by visiting our api.slack page.

If you choose to not take action before November 12, 2025, and your app continues to attempt to use files.upload, your app may break or become unusable.

If you have questions about this change or need help, reach out to us at feedback@slack.com and use the subject line files.upload API deprecation help.

Note: This notification cannot be disabled. You'll continue receiving it until your app stops calling the method.

Read the linked Slack changelog first, then locate the Slackengine bolt code that calls files.upload. Replace that usage with Slack's files.getUploadURLExternal and files.completeUploadExternal flow, and verify the engine's file-upload behavior with the relevant existing checks or tests.