[FEATURE] Preserve original message for merge conflict resolutions

Description
In the dotnet-aicommitmessage tool, which generates commit messages using the ChatGPT API (LLM models), implement a business rule to retain the original commit message when it follows the auto-generated format used during a merge conflict resolution. Currently, the tool replaces all commit messages, which can modify the intended context of merge conflict resolutions. Preserving these original messages will help maintain a clear version history.

Message Pattern
The pattern for auto-generated messages following a merge conflict resolution is as follows:

Merge branch '<source branch>' into <destination branch>
# Conflicts
# file1
# file2
# file3 
# fileN

Requirements

Detect if the commit message follows this pattern, indicating a merge conflict resolution.
Skip generating a new message using the ChatGPT API in these cases and preserve the original message.
Ensure compatibility with C# string manipulation techniques to implement the pattern detection.

Acceptance Criteria

Detect merge conflict resolution messages based on the defined pattern.
Retain the original message for merge conflict resolutions, bypassing the ChatGPT API.
Add unit tests to verify the correct detection of the merge conflict pattern.
Confirm that messages not matching the pattern continue to be processed as usual.

Sample pattern extraction

using System.Text.RegularExpressions;

public class CommitMessageValidator
{
    // Regular expression pattern for merge conflict resolution messages
    private static readonly Regex MergeConflictPattern = new Regex(
        @"^Merge branch '(.+)' into (.+)\n(# Conflicts\n# .+\n?)+$",
        RegexOptions.Multiline | RegexOptions.Compiled
    );

    /// <summary>
    /// Checks if the commit message is an auto-generated merge conflict resolution message.
    /// </summary>
    /// <param name="commitMessage">The commit message to check.</param>
    /// <returns>True if the message matches the merge conflict resolution pattern; otherwise, false.</returns>
    public static bool IsMergeConflictResolutionMessage(string commitMessage)
    {
        return MergeConflictPattern.IsMatch(commitMessage);
    }
}

Additional Context
This feature will help retain the context of conflict resolutions in commit history by preserving the original message format.

guibranco / dotnet-aicommitmessage

[FEATURE] Preserve original message for merge conflict resolutions #113