Add SpeculativePlanManagementEnabled organization setting

[lilincmu]

Description

This PR adds a new organization field, SpeculativePlanManagementEnabled, that can toggle the behavior of Automatically cancel plan-only runs.

Testing plan

1. Generate the required environment variables for go test, TFE_ADDRESS and TFE_TOKEN
2. Run TFE_ADDRESS="https://example" TFE_TOKEN="example" go test ./... -v -run TestOrganizationsUpdate. The tests should pass.

External links

• Jira

Output from tests

Including output from tests may require access to a TFE instance. Ignore this section if you have no environment to test against.

$ TFE_ADDRESS="https://example" TFE_TOKEN="example" go test ./... -v -run TestOrganizationsUpdate
=== RUN   TestOrganizationsUpdate
=== RUN   TestOrganizationsUpdate/with_HCP_Terraform-only_options
=== RUN   TestOrganizationsUpdate/with_new_AggregatedCommitStatusEnabled_option
=== RUN   TestOrganizationsUpdate/with_new_SpeculativePlanManagementEnabled_option
=== RUN   TestOrganizationsUpdate/with_valid_options
=== RUN   TestOrganizationsUpdate/with_invalid_name
=== RUN   TestOrganizationsUpdate/with_agent_pool_provided,_but_remote_execution_mode
=== RUN   TestOrganizationsUpdate/when_only_updating_a_subset_of_fields
=== RUN   TestOrganizationsUpdate/with_different_default_execution_modes
--- PASS: TestOrganizationsUpdate (8.03s)
    --- PASS: TestOrganizationsUpdate/with_HCP_Terraform-only_options (0.77s)
    --- PASS: TestOrganizationsUpdate/with_new_AggregatedCommitStatusEnabled_option (1.50s)
    --- PASS: TestOrganizationsUpdate/with_new_SpeculativePlanManagementEnabled_option (1.36s)
    --- PASS: TestOrganizationsUpdate/with_valid_options (1.06s)
    --- PASS: TestOrganizationsUpdate/with_invalid_name (0.00s)
    --- PASS: TestOrganizationsUpdate/with_agent_pool_provided,_but_remote_execution_mode (0.75s)
    --- PASS: TestOrganizationsUpdate/when_only_updating_a_subset_of_fields (0.59s)
    --- PASS: TestOrganizationsUpdate/with_different_default_execution_modes (1.47s)
PASS
ok      github.com/hashicorp/go-tfe     8.645s
...

[roleesinhaHC]

lgtm!

[ctrombley]

LGTM

[github-actions]

Reminder to the contributor that merged this PR: if your changes have added important functionality or fixed a relevant bug, open a follow-up PR to update CHANGELOG.md with a note on your changes.