SSSD on IPA should fail with short names

[thalman]

SSSD should refuse to start when SSSD is in server mode and full_name_format is set to %1s$.

[gemini-code-assist]

Code Review

This pull request correctly implements a check to prevent SSSD from starting in IPA server mode when full_name_format is set to use only short names. The accompanying test case is also well-written and verifies the new behavior. My only suggestion is to add a system log message for the startup failure to improve visibility for administrators, as the current implementation only logs to the debug log.

[gemini-code-assist]

When SSSD fails to start due to a configuration error, it's crucial to log a message to the system log (e.g., syslog or journald) so that administrators can easily diagnose the problem without needing to enable high-level debug logging. The existing check for a non-default full_name_format already does this using sss_log(). This new fatal error should do the same.

    if (strcmp(be_ctx->domain->names->fq_fmt, "%1$s") == 0) {
        DEBUG(SSSDBG_FATAL_FAILURE, "%s is set to [%s], this is prohibited in server mode!\n",
              CONFDB_FULL_NAME_FORMAT, be_ctx->domain->names->fq_fmt);
        sss_log(SSS_LOG_ERR, "%s is set to [%s], this is prohibited in server mode!\n",
                CONFDB_FULL_NAME_FORMAT, be_ctx->domain->names->fq_fmt);
        return EINVAL;
    }