Update sample projects

[kanej]

Update the sample projects. This work will likely go hand in hand with the documentation rewrites.

We expect there to be multiple sample projects, including:

• javascript sample project with the default setup
• typescript sample project with the default setup
• javascript sample project with the mocha setup
• typescript sample project with the mocha setup
• optimism sample project

[galargh]

The placeholders for the new sample projects were created as part of https://github.com/NomicFoundation/hardhat/pull/5774. We'll need to update and expand them as we implement necessary plugins.