no issue
### Context
As part of updating the theme layer to use members-ssr [here](f9899cb8c4), we introduced a case where if `enableDeveloperExperiments` is not switched on, the whole theme loading will crash due to unavailability of `ssr` property on members service [here](https://github.com/TryGhost/Ghost/blob/master/core/server/services/members/index.js#L12). Since we switch on `enableDeveloperExperiments` by default on master now, the issue won't be reproducible locally until explicitly switched off.
This PR includes a patch fix which adds dummy `ssr` object to members service `api` object and members middleware check on APIs to ensure no crash in case developer flags is not switched on.
Longer term it will be definitely useful to upgrade the dummy `api` object to trigger on member labs than the developer flag.
