lxd/storage: Propagate context

[markylaing]

Part of https://github.com/canonical/lxd/issues/16613#issuecomment-3547843653

Depends on #17016

Note: Context used in deferred functions and revert hooks is always a background context. The context used in an operation is currently a context.TODO but ultimately will be a function on the operation: (*Operation).Context() (e.g. like (*http.Request).Context()).