"attempt-instant-ddl" should support lock_wait_timeout about gh-ost

[hakusaro]

Peering into #1201, I found it perplexing that it says this in the docs:

This is not a problem for most scenarios, but it could be a problem for users that start the DDL during a period with long running transactions.

This is really critical information, in my opinion, because if gh-ost is supposed to be inherently safe, it seems to jeopardize this safety by potentially creating table outages with no controllable timeout here. We primarily introduced gh-ost because of long-running transactions that were hard to pin down and a lack of safety with LHM in these scenarios. While we've mostly cleaned these up, I still think anything that could remotely incur a table outage should have defined characteristics for how long the table will be out.