Open Stack

Hello,

Related change: https://review.openstack.org/#/c/599606

I'd like to push this to stable/rocky because this bug affects me in
production and I'd like to be able to upgrade to rocky to fix this. I
understand that new migrations should not be added to a stable branch
and Renat Akhmerov advised me to ask here to make an exception.

Now for some context on this bug:

The `auth_context` in `delayed_calls_v2` holds the entire catalog
provided by the client to run actions and currently it can hold 64kB on
mysql (JsonDictType => TEXT field).

Some of our customers have a large catalog because we expose many
regions to them and a region weighs around 5kB in our catalog (many
services, long URL for the endpoints...).
So above around 10 regions presented to a project the catalog cannot be
held in the `auth_context` field and no execution can be performed in
mistral from this project.

The change fixes that simply by increasing the maximum size of the field.

So I'm seeking approval from the stable branch team to merge this change.

Thanks,
Pierre