HCS-2061: Add size upgrade field for consul cluster update

[ellacai]

Changes

• remove ForceNew on consul cluster size field - we want to update the resource instead of destroy and recreate
• modify resourceConsulClusterUpdate to handle size change
• note: the logic to validate size upgrade paths is already in consul service so it is not needed here

Testing

• tested size upgrade using terraform with consul cluster in integration (currently behind launchdarkly flag)

Acceptance Criteria:

• HCP TF provider should call the consul-service update cluster API on a change in the value for size , instead of re-creating the cluster.
• The PR should be approved from a consul-service engineer and a TCE team engineer
• PR will not be merged until monitoring is added

[hashicorp-cla]

All committers have signed the CLA.

[lackeyjb]

This looks good, but could we add some updates to the acceptance tests for this change?

[lackeyjb]

Looks good 👍