enable support for dns_opt in compose again

[jeroenpeeters]

I found that in docker-compose v3 the dns_opt option was not enabled in the config_schema. The option however is correctly passed to the Docker CLI. A test even still exists for this, see tests/integration/service_test.py test_dns_opt_value.

This PR enables the dns_opt again. The schema is a copy from v3.7 with the addition of dns_opt on line 133.

Tested against Docker version 18.09.1, build 4c52b90.

Resolves

• Implement dns_opt in version 3 #5010
• dns_option missing from compose schema cli#1557

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "master" git@github.com:jeroenpeeters/compose.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[ijc]

This PR enables the dns_opt again. The schema is a copy from v3.7 with the addition of dns_opt on line 133.

Thanks, but if I understand the discussion on #5010 correctly then what we need is for docker/cli#1557 to first be resolved on the cli repo, which will update the appropriate ./cli/compose/schema/data/config_schema_v3.*.json in that repository and then we can sync that schema change to here.

We should not, AIUI, be declaring new schema versions in this repo as is being done in this PR.

[ijc]

BTW see #6642 for an attempt at a resync (and the problems caused by editing things directly here).

[phyrwork]

Looks like this has been done since 1.27.0.

[ndeloof]

dns_opt indeed has been re-introduced in compose spec.
Closing this PR as "obsolete"