[Bug] Update buildkite pipeline to only run steps based on files changed in the repository

[matoszz]

We pay for minutes on buildkite's hosted runners, so should not run builds unnecessarily. For example, when opening this PR which added a new file to our .github/ directory, we ran an entire build / build pipeline (https://buildkite.com/theopenlane/core/builds/1568) unnecessarily.

Pipeline configuration should execute steps for pre-check, etc., based on modified files in the repository so things like README.md changes, .github/ changes, etc., should not kick off any steps (or at least be constrained to the steps requisite the change)