Jacamar CI v0.26.1

Bug & Development Fixes

Establish job behavior overriding interface and fix credential.store (!618, !619)
- The core reason for these changes was adjusting to new behavior in the runner that began removing the job’s .git/config file during the get_sources script, after we had attempted to inject a number of default configurations.
- The crucial portion of this change is the introduction of the Overrider interface that will maintain the responsibility for modifying GitLab Runner behaviors (e.g., job scripts) in a more formal and easily maintainable manner moving forward.