Fix pins of ocluster & ocurrent in Dockerfile & .opam file

[ElectreAAS]

This PR is the third one in the series of committing/cleaning what was on the prod server. There were pins on art-w/ocluster even though that repo isn't actively maintained. Part of the pin actually made sense, as the package ocluster-worker isn't merged into the main branch yet, so I added a comment to specify when to remove the pin.

Another weird thing is the line sudo ln -f /usr/bin/opam-2.1 /usr/bin/opam. This (AFAIK) forces the used version of opam to be 2.1 instead of the default 2.0. Why this change was made in the first place I don't really know, but there might be someone down the line assuming opam version to be 2.1 so better not change this without full knowledge

[punchagan]

@art-w Could you look at this PR since the changes are very similar to what you did in #380, and I don't understand what the best way forward here is.

[art-w]

Yes it finally works! Good job :) Do you know if the omigrate "dirty" column schema update is still required ? (for example would @punchagan run into the issue of the missing column?)

[ElectreAAS]

Do you know if the omigrate "dirty" column schema update is still required ?

Probably yes. I don't really know where to start to fix this in the database description side. Just in case, here's the SQL line to be run if one where to encounter the "dirty" error locally: ALTER TABLE schema_migrations ADD dirty boolean NOT NULL DEFAULT false;

[art-w]

Thanks! Let's hope omigrate fixes their own schema migration, but otherwise it's not a big deal :)