feat: add show_footer config option to hide footer

[FernandoCelmer]

Description

• mkdocs_dracula_theme/mkdocs_theme.yml: added show_footer: true as a default config key
• mkdocs_dracula_theme/base.html: wrapped the footer include block with {% if config.theme.show_footer %} conditional

Motivation and Context

Users who want to hide the "Made with Dracula Theme for MkDocs" footer had no native way to do so. Setting show_footer: false in mkdocs.yml now suppresses it cleanly without requiring a custom_dir override.

Closes #28

Types of changes

• Bug fix
• New feature
• Documentation

Checklist

• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• I have updated the CHANGELOG
• I have updated the documentation accordingly

[FernandoCelmer]

Reopening with correct branch naming convention.