error message unclear when running `shore save` when cert is missing

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### Description

Original Author: schammah

``` ~/go/bin/shore save 11:17:14
WARN[0000] Save pipeline returned an errorno such file or directory
no such file or directory
```

error due to missing certificates file from spin config is unclear

### Steps to Reproduce

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**Expected behavior:**

**Actual behavior:**

**Reproduces how often:**

### Versions

### Additional Information

Start by reproducing `shore save` with the certificates file missing from the spin config, then trace where the generic `no such file or directory` error is produced. Done means the command clearly identifies the missing certificates file and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.