Use next minor version with beta suffix for prereleases

- Changed prerelease versioning to increment minor version instead of using last tag
- Changed suffix from "preview" to "beta"
- Format is now {NEXT_MINOR_VERSION}-beta.{COMMIT_COUNT}
- Example: 0.43.0-beta.123 (if last tag is 0.42.x)
- Updated documentation in NUGET_RELEASE.md and TESTING.md

Co-authored-by: adamhathcock <527620+adamhathcock@users.noreply.github.com>

build/Program.cs

@@ -280,7 +280,7 @@ static (string version, bool isPrerelease) GetVersion()
     }
     else
     {
-        // Not tagged - create prerelease version based on last tag
+        // Not tagged - create prerelease version based on next minor version
         var allTags = GetGitOutput("tag", "--list")
             .Split('\n', StringSplitOptions.RemoveEmptyEntries)
             .Where(tag => Regex.IsMatch(tag.Trim(), @"^\d+\.\d+\.\d+$"))
@@ -288,10 +288,14 @@ static (string version, bool isPrerelease) GetVersion()
             .ToList();
 
         var lastTag = allTags.OrderBy(tag => Version.Parse(tag)).LastOrDefault() ?? "0.0.0";
+        var lastVersion = Version.Parse(lastTag);
+
+        // Increment minor version for next release
+        var nextVersion = new Version(lastVersion.Major, lastVersion.Minor + 1, 0);
 
         var commitCount = GetGitOutput("rev-list", "--count HEAD").Trim();
 
-        var version = $"{lastTag}-preview.{commitCount}";
+        var version = $"{nextVersion}-beta.{commitCount}";
         Console.WriteLine($"Building prerelease version: {version}");
         return (version, true);
     }