[FEATURE] show error/warning in createDeltaPkg if source is missing commits already present on target branch

[JoernBerkefeld]

in short, check if git log reveals that target branch should first get merged into source branch:
git log --oneline feature-branch..origin/main

something like this should do the trick:

const simpleGit = require('simple-git');
 
// Initialize simple-git
const git = simpleGit();
 
// Function to check if there are commits on `main` that are not in the feature branch
async function checkCommits() {
  try {
// Fetch the latest changes specifically for the remote 'main' branch
     await git.fetch('origin', 'main');
 
    // Run the `git log` command to check for commits on `main` not in the feature branch
    const log = await git.log(['feature-branch..origin/main']);
 
    // If there are commits, advise the user to merge `main` into the feature branch
    if (log.total > 0) {
      console.log("There are commits in the 'main' branch that are not in your feature branch.");
      console.log("Please merge 'main' into your feature branch first to avoid unintended merge outcomes.");
    } else {
      console.log("Your feature branch is up to date with 'main'. You can proceed with merging.");
    }
  } catch (err) {
    console.error('Error checking commits:', err);
  }
}
 
// Run the function
checkCommits();

not sure if fetching is always wanted though.