Add support for automatic CSRF token injection

[lcnicolau]

Closes #36

Support secure CSRF protection for htmx-driven requests across all relevant HTTP methods.

Changes:

• Minor updates to existing HtmxAttributeProcessor to make it easier to extend.
• Created HtmxCsrfAttributeProcessor (with @since 5.1.0 annotation) to handle CSRF token injection.
• Updated HtmxDialect to associate the new processor with post, put, patch, and delete attributes.
• Added unit tests and updated README.md.

Implementation Notes:

• Commit 1: Uses hx-vals to send the CSRF token. However, DELETE requests expose the token in query parameters.
• Commit 2: Switches to hx-headers, which is more secure and aligns with htmx recommendation.
• Both commits are kept for reference, but can be squashed if preferred.