[Bug]: Pre-0.19.27 CLI on post-0.19.27 server, default the `working_dir` into `/` instead of `/workflow`

[peterschmidt85]

Steps to reproduce

1. Run the post-0.19.27 server
2. Install pre-0.19.27 CLI
3. Create a run configuration without working_dir set
4. Apply the configuration

Actual behaviour

1. The working_dir is set to /

Expected behaviour

1. The working_dir is set to /workflow

dstack version

cli - 0.19.21; server - 0.19.34

Server logs

Additional information

No response

[peterschmidt85]

What happens:

1. CLI sets working_dir to None
2. Server propagates None to Runner

   dstack/src/dstack/_internal/server/services/jobs/configurators/base.py

   Line 329 in bd9fe78

   if working_dir is None:

3. Runner, it uses Docker image current working dir:

   dstack/runner/internal/executor/executor.go

   Line 358 in bd9fe78

   if ex.jobSpec.WorkingDir == nil {

What should happen (until we drop the legacy working dir):

1. Runner, if ex.jobSpec.WorkingDir is nil, should set it to consts.LegacyRepoDir