Rename variables to workspace_variables in create mutation

MR: Rename variables to workspace_variables in crea... (!188937 - merged)

Description

We should rename the argument variables to workspace_variables in the workspaceCreate mutation because we want to be consistent about the argument name and the returned field name from the workspaces query.

Since renaming an argument is a breaking change according to the graphQL docs, we need to follow the deprecation process and mark the variables argument for deprecation.

This is based on the discussion here: !184854 (comment 2401850882)

Acceptance criteria

• New workspace_variables argument introduced on mutation.workspaceCreate
• New workspace_variables argument marked as experiment
• Old variables argument deprecated on mutation.workspaceCreate
• Graphql docs updated
• Necessary follow-up issues created according to our process

References

• workspacevariableinput
• mutationworkspacecreate
• Graphql deprecation and removal