[RFE] Variable to explicitly control full/diff scan

[zabbal]

By default semgrep-action scans only the diff added in the PR. That's very neat optimization and it probably should stay that way by default.

However for the projects just adopting semgrep CI integration it would be great to be able to explicitly configure full source code scan for CI running on PR.

Right now it's possible by changing trigger event to "push" instead of "pull_request" and switching scan policy to blocking mode but that's far from obvious for newcomers.

Having explicit variable (similar to 'auditOn' for example) to select between full and partial scans (defaulting to partial to preserve the current behavior) would be great to streamline initial integration.

[mykter]

Right now it's possible by changing trigger event to "push" instead of "pull_request" and switching scan policy to blocking mode

And for GitLab, it looks like it's not possible at all. ref #352