chore: undeprecate the workspace rename flag and clarify potential issues (#21669)

This undeprecates the `allow-workspace-renames` flag. IIUC, the 'danger'
with using this flag is that the workspace name might have been used in
the definition of some other terraform resources within template code,
so a rename could cause problems such as with persistent disks.

for https://github.com/coder/coder/issues/21628

---------

Signed-off-by: Callum Styan <callumstyan@gmail.com>

docs/admin/templates/extending-templates/resource-persistence.md

@@ -57,6 +57,8 @@ To prevent this, use immutable IDs:
 - `coder_workspace.me.owner_id`
 - `coder_workspace.me.id`
 
+You should also avoid using `coder_workspace.me.name` if your deployment allows workspace renaming via `CODER_ALLOW_WORKSPACE_RENAMES` or `--allow-workspace-renames`.
+
 ```tf
 data "coder_workspace" "me" {
 }

docs/reference/cli/server.md

@@ -1311,7 +1311,7 @@ The renderer to use when opening a web terminal. Valid values are 'canvas', 'web
 | YAML        | <code>allowWorkspaceRenames</code>          |
 | Default     | <code>false</code>                          |
 
-DEPRECATED: Allow users to rename their workspaces. Use only for temporary compatibility reasons, this will be removed in a future release.
+Allow users to rename their workspaces. WARNING: Renaming a workspace can cause Terraform resources that depend on the workspace name to be destroyed and recreated, potentially causing data loss. Only enable this if your templates do not use workspace names in resource identifiers, or if you understand the risks.
 
 ### --health-check-refresh