Add support for retry_transient_errors to then CLI

[djmcgreal-cc]

Description of the problem, including code/CLI snippet

I'm using the gitlab cli against gitlab.com which is producing transient errors. The API has the ability to retry these but it looks like the CLI code misses the option because merge_config doesn't cover the field.

Expected Behavior

Ideally the cli would have a command line parameter, but it should definitely respect the configuration file.

Actual Behavior

No ability to turn on retries with the CLI.

Specifications

• python-gitlab version: 4.4
• API version you are using (v3/v4): v4
• Gitlab server version (or gitlab.com): .com