feat(plugin-url)!: initial release

[shellscape]

Component / Package Name:

@jsx-email/plugin-url

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

N/A

Description

Adds @jsx-email/plugin-url, a new plugin for modifying URLs in rendered email HTML.

The initial feature is append, which appends URL parameters to matching URL attributes. It supports Maizzle-style
behavior without adding any default jsx-email render integration. Users opt in by adding urlPlugin(...) to their
config plugins array.

Included behavior:

• Defaults to processing a tags.
• Defaults to URL attributes src, href, poster, srcset, and background.
• Defaults to strict URL matching.
• Defaults to unencoded query parameter serialization.
• Correctly inserts ? for URLs without query strings and & for URLs with existing query strings.
• Preserves URL fragments.
• Supports custom tags, selector-based tags, custom attributes, srcset, strict mode, and query string encoding.

This also adds plugin documentation and sidebar entries for the URL Plugin.