backend/oss: Removes the ConflictWith tag which on the attributes assume_role* to fix the incompatible error

Cloud: Update Workspace during Tags strategy

command: Update backend hash value only after a successful migration

The Meta.backend_C_r_S_unchanged() method was sadly a bit of a mess.

It seems to have originally been used as a method to be called
when the backend is not changing, with an extra assumption that if the
configured backend's hash doesn't match the one in state, surely the
hash should just be updated as an option might have been moved to
command line flags.

However, this function was used throughout this file as 'the method to
load the initialized (but not necessarily configured) backend',
regardless of whether or not it is the same (unchanged). This is in
addition to Meta.backendFromState(), which is used to load the same
thing except in the main codepath of 'init -backend=false'.

These changes separate the concerns of backend_C_r_S_unchanged() by

1) Fetching the saved backend (savedBackend())
2) Updating the hash value in the backend cache when appropriate (either
   by leaving it to the caller to do themselves or by calling
   updateSavedupdateSavedBackendHash())

This allows migration codepaths to *not* update the hash value until
after a migration has successfully taken place.

Pulled and updated from
https://github.com/hashicorp/terraform/pull/26260

* command/format: fix list nested attr diff rendering

Previously, diffs only rendered correctly if all changed elements
appeared before all unchanged elements. Once an unchanged element was
found, all remaining elements were skipped. This usually led to the
output being an empty list with a weird amount of space between the
brackets.

* command/format: improve list nested attr rendering

This makes several changes that make diffs for lists clearer and more
consistent:

  * Separate items with brackets instead of only new lines. This better
    matches the input syntax and avoids confusion from the first and
    last brackets implying there is a single item.
  * Render an action symbol for each element of the list
  * Use the correct action symbol for new and deleted items
  * Fix the alignment of opening and closing brackets

I also refactored the structure so it is similar to the set and map
cases to minimize duplication of the new prints.

* Fix re-use of blockBodyDiffResult struct

configs: fix ignore_changes config override bug

cloud: Allow cloud tests to be run in parallel

backend/oss: Supports the new attribute sts_endpoint

nullable variable docs

Co-authored-by: Laura Pacilio <83350965+laurapacilio@users.noreply.github.com>

Co-authored-by: Laura Pacilio <83350965+laurapacilio@users.noreply.github.com>

Co-authored-by: Laura Pacilio <83350965+laurapacilio@users.noreply.github.com>

Co-authored-by: Laura Pacilio <83350965+laurapacilio@users.noreply.github.com>

Add the `-parallel N` switch to tell the tests to run in N processes:

```
TFE_TOKEN=$TFE_TOKEN TFE_HOSTNAME=$TFE_HOSTNAME TF_ACC=1 go test -v \
  -tags=e2e ./internal/cloud/e2e/... -parallel 4
```

Add `nullable` to the variable documentation.
Remove "module" from the "null means omission" part of the null type
documentation.

Previously, `terraform init` was throwing an error if you configured the cloud
block with `tags` and there weren't any tagged workspaces yet. Confusing and
alienating, since that that's a fairly normal situation! Basically TFC was
handling an empty list of workspaces worse than other backends, because it
doesn't support an unnamed default workspace.

This commit catches that condition during `Meta.selectBackend()` and asks the
user to pick a name for their first tagged workspace. If they cancel out, we
still error, but if we know what name they want, we can handle it the same way
as a nonexistent workspace specified in `name` -- just pass it to
`Meta.SetWorkspace()`, and let the workspace get implicitly created when
`InitCommand.Run()` eventually calls `StateMgr()`.

configs: explicitly nullable variable values

Co-authored-by: Laura Pacilio <83350965+laurapacilio@users.noreply.github.com>

This is documentation for the first set of refactoring-related features,
all based on the new "moved" blocks in the Terraform language.

I've named the documentation section "refactoring" because in previous
discussions with users that seems to be the term they use to describe the
underlying need.

"moved" blocks are our first language feature intended to meet that need,
although it probably won't be the last as we consider other requirements
in later releases. My intent here is that once we've published this it
should eventually end up being the first result for a web search for the
topic of Terraform refactoring.

Based on feedback during earlier alpha releases, we've decided to move
forward with the current design for the first phase of config-driven
refactoring.

Therefore here we've marked the experiment as concluded with no changes
to the most recent incarnation of the functionality. The other changes
here are all just updating test fixtures to no longer declare that they
are using experimental features.

cloud: Fix prerelease version constraint checks

command: Adjust skipping of resource counts for any remote implementation

Flatten `assume_role` block for OSS backend