Remove incompatible balancing_mode

[wiktorn]

balancing_mode review.

net-lb-int

• Fix error on apply of example:

Error creating RegionBackendService: googleapi: Error 400: Invalid value for field 'resource.backends[0].balancingMode': 'UTILIZATION'. Balancing mode must be CONNECTION for an INTERNAL backend service., invalid

• remove unused balancing_mode variable, as only one value is possible anyhow

net-lb-ext

• update in the backends description

net-lb-proxy-int

• update in the backends description

net-lb-app-int

• added validation of balancing_mode
• fixed other validations

net-lb-app-ext

• added validation of balancing_mode
• fixed other validations
• removed validation for locality_lb_policy as this variable is not used in this module

Closes: #1767

Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[ludoo]

Great catch. As you were saying in chat, we might want to not even expose balancing mode anymore.

[wiktorn]

Great catch. As you were saying in chat, we might want to not even expose balancing mode anymore.

This went a bit bigger as I followed the white rabbit. Please re-check.

[ludoo]

great stuff