Hardhat 3 plugin development docs

[alcuadrado]

This issue is a live TODO of the different sections that are missing from the plugin development docs.

The terminology (Tutorial, Guide/How-to, Reference, and Explanation) is based on the Diátaxis conceptual framework, which we use across all the documentation.

They are in priority order:

TODO

• Guides > Migrating a Hardhat 2 plugin [p0]
• Reference > Hooks and Hook Handlers [p0]
• Reference > Task definitions [p0]
• Guides > Hooking into the compilation process [p1]
• Guides > Using conditional dependencies [p1]
• Explanations > Multichain plugins [p1]
• Guides > Extending the Hardhat config [p1]
• Explanations > Tasks [p1]
• Explanations > Global options [p1]
• Explanations > User interruptions [p2]
• Guides > Handling I/O from Hook Handlers [p2]
• Guides > Using Dynamic Hook Handlers [p2]

Using the boilerplate .md files

The markdown files for all of this sections are already created in src/content/plugin-development. You just have to find the one you want to work on, remove the .ignore from its name, and uncomment its entry in its directory's _dirinfo.yaml.