Lower default progress_bar_refresh_rate
🚀 Feature
From a conversation in Slack.
In v0.7.1, the default value of  progress_bar_refresh_rate is 50, which I think too high.
It is a measure to prevent notebook freezing, however, I believe most users run PL on CLI.
In addition, the high default value confuses the users in fast_dev_run because it has only 2 iterations.
So, I suggest the following:

Set the default value as 1 or 2. (I think 1 is better.)
Add doc for notebook users like "you should raise progress_bar_refresh_rate to prevent freezing!"

for participants of the conversation: @williamFalcon @Borda @jeremyjordan