PSS: Update the workspace new subcommand to work with PSS, add E2E and integration tests for using workspace commands with PSS.

[SarahFrench]

(Stacked on top of #37790, due to needing simple6 implementations of PSS for E2E testing)

This PR introduces a bunch of testing to show that the workspace commands work in combination with pluggable state storage. There is both an integration test and an E2E test showing that PSS can be used in the context of this sequence of actions:

• Running init to create a default workspace
• Creating a custom workspace
• Listing all workspaces present
• Selecting a different workspace
• Showing the selected workspace
• Deleting a workspace

In this PR I also updated how workspace new is implemented. This new code comment explains how the command previously achieved creating a new workspace:

terraform/internal/command/workspace_new.go

Lines 99 to 106 in 55a606d

	// Create the new workspace
	//
	// In local, remote and remote-state backends obtaining a state manager
	// creates an empty state file for the new workspace as a side-effect.
	//
	// The cloud backend also has logic in StateMgr for creating projects and
	// workspaces if they don't already exist.
	sMgr, sDiags := b.StateMgr(workspace)

Pluggable state stores intentionally don't have side-effects in the same way, and instead Terraform is expected to create the state file explicitly. I've updated the workspace new command to identify when PSS is in use and to only attempt to create the state file when that's the case. Due to this there isn't an issue of state files being 'created twice' etc when PSS isn't in use.

Target Release

1.15.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

[SarahFrench]

Found a bug during this work 🐛

[SarahFrench]

I imagined that future E2E tests related to PSS would all go in this file.