[Bug]: New logs API breaks backward compatibility with`dstack logs`

[r4victor]

Steps to reproduce

1. Use server from master and cli 0.19.18
2. Start a run and try to read its logs with dstack logs. You'll get an error because the old CLI tries to decode base64-encoded logs but the server returns logs in plaintext (after [Feature] Strip ANSI codes from run logs and store them as plain text instead of bytes  #2876)

dstack logs selfish-owl-2
Traceback (most recent call last):
  File "/Users/r4victor/Projects/dstack/venvt/bin/dstack", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/Users/r4victor/Projects/dstack/venvt/lib/python3.12/site-packages/dstack/_internal/cli/main.py", line 91, in main
    args.func(args)
  File "/Users/r4victor/Projects/dstack/venvt/lib/python3.12/site-packages/dstack/_internal/cli/commands/logs.py", line 46, in _command
    for log in logs:
               ^^^^
  File "/Users/r4victor/Projects/dstack/venvt/lib/python3.12/site-packages/dstack/api/_public/runs.py", line 227, in logs
    yield base64.b64decode(log.message)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.12/3.12.9/Frameworks/Python.framework/Versions/3.12/lib/python3.12/base64.py", line 88, in b64decode
    return binascii.a2b_base64(s, strict_mode=validate)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
binascii.Error: Incorrect padding

Actual behaviour

No response

Expected behaviour

No response

dstack version

master

Server logs

Additional information

No response

[r4victor]

Closed by #2910