Slack integration does populate all channels in dropdown

[tomas-tts]

The Slack integration list all the slack channels from the dropdown, although previously it listed only channel where looker-bot was invited as a channel participant.

The issue is the Slack integration takes long time to respond and sometimes is not responding at all. I guess the reason is its reading all slack channels metadata.

[teka23]

It looks like it was decided to use user.conversations in https://github.com/looker-open-source/actions/pull/472/files
But, it got reverted back to convesations.list in https://github.com/looker-open-source/actions/pull/505/files#diff-b667a263df720f03b47241dd0837b7fbba562197e03a40b28af929daa41bf82d
@phillipperalez Was there any reason for this change?