Add enterprise check for new Raft Autopilot parameter

[vinay-gopalan]

In v3.12.0 we added a new parameter to the Raft Autopilot resource disable_upgrade_migration. There was a bug introduced due to the field having a default value of false written to Vault, and since this is an enterprise field this was breaking the TF config s for non-enterprise users. The improvements made in this PR fix the bug and also add some utils to the provider package to check for enterprise servers.

Fixes #1718

Output from acceptance testing:

=== RUN   TestAccRaftAutopilotConfig_basic
--- PASS: TestAccRaftAutopilotConfig_basic (2.59s)
PASS

=== RUN   TestIsEnterpriseSupported
=== RUN   TestIsEnterpriseSupported/not-enterprise
=== RUN   TestIsEnterpriseSupported/enterprise-hsm
=== RUN   TestIsEnterpriseSupported/enterprise
--- PASS: TestIsEnterpriseSupported (0.00s)
    --- PASS: TestIsEnterpriseSupported/not-enterprise (0.00s)
    --- PASS: TestIsEnterpriseSupported/enterprise-hsm (0.00s)
    --- PASS: TestIsEnterpriseSupported/enterprise (0.00s)
PASS

[fairclothjm]

LGTM