Slack Plugin Doesn't Truncate large messages

[phall-teleport]

Expected behavior: Slack plugin should truncate a message that is otherwise too large for the Slack API

Current behavior: User receives an request error from Teleport

Bug details:

• Teleport version
• Recreation steps
• send a 2kb message through Slack Plugin
• Debug logs

  ERRO   Failed to process request error:[
  ERROR REPORT:
  Original Error: trace.aggregate invalid_blocks, invalid_blocks, invalid_blocks, invalid_blocks, invalid_blocks
  Stack Trace:
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/access/slack/bot.go:155 [github.com/gravitational/teleport/integrations/access/slack.Bot.BroadcastAccessRequestMessage](http://github.com/gravitational/teleport/integrations/access/slack.Bot.BroadcastAccessRequestMessage)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/access/accessrequest/app.go:268 [github.com/gravitational/teleport/integrations/access/accessrequest.(*App).broadcastAccessRequestMessages](http://github.com/gravitational/teleport/integrations/access/accessrequest.(%2AApp).broadcastAccessRequestMessages)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/access/accessrequest/app.go:209 [github.com/gravitational/teleport/integrations/access/accessrequest.(*App).onPendingRequest](http://github.com/gravitational/teleport/integrations/access/accessrequest.(%2AApp).onPendingRequest)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/access/accessrequest/app.go:159 [github.com/gravitational/teleport/integrations/access/accessrequest.(*App).onWatcherEvent](http://github.com/gravitational/teleport/integrations/access/accessrequest.(%2AApp).onWatcherEvent)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/lib/watcherjob/watcherjob.go:274 [github.com/gravitational/teleport/integrations/lib/watcherjob.job.eventLoop.job.eventFuncHandler.func1](http://github.com/gravitational/teleport/integrations/lib/watcherjob.job.eventLoop.job.eventFuncHandler.func1)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/lib/process.go:209 [github.com/gravitational/teleport/integrations/lib.jobFunc.DoJob](http://github.com/gravitational/teleport/integrations/lib.jobFunc.DoJob)
  /go/pkg/mod/github.com/gravitational/teleport@v0.0.0-20240112170115-542fbb04b39d/integrations/lib/process.go:97 [github.com/gravitational/teleport/integrations/lib.NewProcess.func2.1](http://github.com/gravitational/teleport/integrations/lib.NewProcess.func2.1)
  /usr/local/go/src/runtime/asm_amd64.s:1650 runtime.goexit
  User Message: invalid_blocks, invalid_blocks, invalid_blocks, invalid_blocks, invalid_blocks] request_id:0190c7b4-cbac-7535-90d1-b28af0033633 request_op:put request_state:PENDING accessrequest/app.go:168

[shuaichang]

+1 on this issue, the Slack integration used to work but stopped working recently. It has been pretty useful for us, will there be a timeline when this can be fixed?