feat: make conventionalcommits default preset

[babblebey]

This pull request updates the default commit message parsing preset from angular to conventionalcommits, aligning the project with the Conventional Commits specification.

Changes Made

• Updated the implementation in lib/load-parser-config.js to use conventional-changelog-conventionalcommits as the default preset instead of conventional-changelog-angular. [1] [2]
• Replaced conventional-changelog-angular with conventional-changelog-conventionalcommits in runtime dependencies in package.json.
• Updated integration and unit tests to expect conventionalcommits as the default preset instead of angular, ensuring test coverage matches the new behavior. [1] [2]
• Changed the default preset in the README.md documentation from angular to conventionalcommits, clarifying expected behavior for users.

Related Issue

Fixes semantic-release/semantic-release#3406