[DOCS] Document app.param() and Router.param() in API docs

[asos-craigmorten]

Issue

Add API documentation for newly implemented app.param() and Router.param() APIs

Details

Add the documentation to the the API docs found in the ./.github/API/ directory. Generally documentation can be lifted fairly seamlessly, but take care to:

• follow the current Opine docs style
• refer to Express only when demonstrating influence / referring to original source for legal or drawing comparison, otherwise use Opine
• use ts over js for files and code blocks

Express Docs:

• https://expressjs.com/en/4x/api.html#app.param
• https://expressjs.com/en/4x/api.html#router.param

Express Docs Src:

• https://raw.githubusercontent.com/expressjs/expressjs.com/gh-pages/_includes/api/en/4x/app-param.md
• https://raw.githubusercontent.com/expressjs/expressjs.com/gh-pages/_includes/api/en/4x/router-param.md