state/remote: Generate error when force push is requested but not supported

[chrisroberts]

Currently when attempting to force push a remote state to a backend which
has not implemented the ClientForcePusher, the force option is ignored and
state verification is applied like normal. This checks if the force option
was given, and if the client does not implement the ClientForcePusher interface
it returns an error that the backend does not support the option.

Current behavior:

$ terraform state push -force ./old.tfstate
Failed to write state: cannot import state with serial 34 over newer state with serial 36

Proposed behavior:

$ terraform state push -force ./old.tfstate
Failed to write state: The configured backend does not support forced state push.

[codecov]

Codecov Report

Merging #26042 into master will decrease coverage by 0.00%.
The diff coverage is 75.00%.

Impacted Files	Coverage Δ
backend/remote-state/inmem/client.go	95.23% <0.00%> (-4.77%)	⬇️
states/remote/state.go	67.92% <100.00%> (+0.61%)	⬆️
terraform/node_resource_plan.go	91.80% <0.00%> (-1.64%)	⬇️
dag/marshal.go	54.44% <0.00%> (+1.11%)	⬆️

[pselle]

@chrisroberts I think what you have here was related to a bug that was fixed not long after your PR: #26190

I think this means the behavior you're describing has changed? Let us know if you want to continue to pursue this PR in some fashion.

[hashicorp-cla]

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