fix: revert psc_config workaround - causes permanent drift

[KelvinVenancio]

Problem

PR #718 was a temporary workaround for a provider bug, but now causes permanent drift:

# Every terraform plan shows this, even when PSC is disabled:
+ psc_config {
    + allowed_consumer_projects = []
    + psc_enabled               = false
  }

Root cause: Workaround forces psc_config creation via ["psc_disabled"], but GCP API omits the block when PSC is disabled → constant state mismatch.

Solution

The original provider issue is fixed, reverting to the original behavior:

- for_each = ip_configuration.value.psc_enabled ? ["psc_enabled"] : ["psc_disabled"]
+ for_each = lookup(ip_configuration.value, "psc_enabled", false) ? [1] : []

Testing Results

✅ psc_enabled = false → No drift, no unnecessary blocks
✅ psc_enabled = true → Proper block creation
✅ No PSC config → No drift, clean plans

Before: terraform plan always shows psc_config changes
After: terraform plan shows "No changes" when appropriate

Reverts: #718 | Resolves: #750

What do you guys think?

Thanks.

[imrannayer]

/gcbrun