Improve final backporting result reports

[lampajr]

Is your feature request related to a problem? Please describe.
Right now if something went wrong, we list all failures that occurred without linking it to the specific target branch to which it is associated with. This could be annoying when there are many issues or long errors.

Describe the solution you'd like
As final step, returns a <target-branch, result> report such that it clearly states which backport failed and which did not.

For instance, something in tabular format:

Target Branch	Result	Error
develop	OK	-
prod	KO	error: ....

Describe alternatives you've considered
n/a

Additional context
This could also be added in the failure comment added in the original pull request

[lampajr]

It should be probably enough to keep track of the target-branch associated to the occurred failure here

git-backporting/src/service/runner/runner.ts

Lines 84 to 104 in 2b4b429

	const failures: string[] = [];
	// we need sequential backporting as they will operate on the same folder
	// avoid cloning the same repo multiple times
	for(const pr of backportPRs) {
	try {
	await this.executeBackport(configs, pr, {
	gitClientType: gitClientType,
	gitClientApi: gitApi,
	gitCli: git,
	});
	} catch(error) {
	this.logger.error(`Something went wrong backporting to ${pr.base}: ${error}`);
	if (!configs.dryRun && configs.errorNotification.enabled && configs.errorNotification.message.length > 0) {
	// notify the failure as comment in the original pull request
	let comment = injectError(configs.errorNotification.message, error as string);
	comment = injectTargetBranch(comment, pr.base);
	await gitApi.createPullRequestComment(configs.originalPullRequest.url, comment);
	}
	failures.push(error as string);
	}
	}