Backup fails with rootless deployment

[mmomjian]

I suspect we need to add /.cache as a mount to docker-compose.rootless.yml

unable to open cache: mkdir /.cache: permission denied
restic exited with code 1: mkdir /.cache: permission denied github.com/restic/restic/internal/backend/cache.New /restic/internal/backend/cache/cache.go:89 github.com/restic/restic/internal/global.setupCache /restic/internal/global/global.go:423 github.com/restic/restic/internal/global.OpenRepository /restic/internal/global/global.go:333 main.runUnlock /restic/cmd/restic/cmd_unlock.go:51 main.newUnlockCommand.func1 /restic/cmd/restic/cmd_unlock.go:33 github.com/spf13/cobra.(*Command).execute /home/build/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1015 github.com/spf13/cobra.(*Command).ExecuteC /home/build/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1148 github.com/spf13/cobra.(*Command).Execute /home/build/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1071 github.com/spf13/cobra.(*Command).ExecuteContext /home/build/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1064 main.main.func2 /restic/cmd/restic/main.go:189 main.main /restic/cmd/restic/main.go:197 runtime.main /usr/local/go/src/runtime/proc.go:290 runtime.goexit /usr/local/go/src/runtime/asm_amd64.s:1771