hlx up without config should render with helix-pages code

[tripodsan]

when running hlx up with no helix-config.yaml nor a src directory, the project should render using the fallback code from https://github.com/adobe/helix-pages.

The code should be provided via an npm package, so that it is stable in respect to semver when installing helix-cli, but also allows to update if needed. alternatively, hlx up could automatically download the code from github.

Suggestion

- [ ] create a `@adobe/helix-pages` npm package that contains the `src` and `htdocs` folder. - [ ] add `@adobe/helix-pages` as `dependency` to `helix-cli` - [ ] `hlx up` will check if a fallback code repository is needed, and if so, it will ensure that the packaged code is used for rendering. eg: 1. set the `code` and `static` repository to `${hlx-cli-installpath}/node_modules/@adobe/helix-pages` 2. set the source directory to `${hlx-cli-installpath}/node_modules/@adobe/helix-pages/src`

• hlx up will check if a fallback code repository is needed, and if so, it will ensure that the
  helix-pages repository is checked out to .hlx/pages/master and the code is used for rendering. eg:
  1. set the static repository to .hlx/pages/master
  2. set the source directory to .hlx/pages/master/src

[tripodsan]

In a discussion with @davidnuescheler we thought that it might be better and more transparent to checkout the helix-pages repo into the .hlx/pages directory. this allows for easy retrieval of the latest code.

[tripodsan]

the current helix pages tries to include a header and footer md. running this on an empty projects shows ugly errors:

$ hlx up
    __ __    ___       ___
   / // /__ / (_)_ __ / _ \___ ____ ____ ___
  / _  / -_) / /\ \ // ___/ _ `/ _ `/ -_|_-<
 /_//_/\__/_/_//_\_\/_/   \_,_/\_, /\__/___/
                              /___/ v4.0.6

Checking out sources from https://github.com/adobe/helix-pages.git#master
Debugger listening on ws://127.0.0.1:9229/52db01ac-d13f-43df-959e-6f5ca6201f94
For help, see: https://nodejs.org/en/docs/inspector
Building project files...done 1081ms
[hlx] info: Starting helix-simulator v2.12.11
[hlx] info: Local Helix Dev server up and running: http://localhost:3000/
[git] info: [98433] HTTP: listening on port 57091
[hlx] error: Could not find Markdown at http://127.0.0.1:57091/raw/helix/localhost--local--default/master/header.md
[hlx] error: Could not find Markdown at http://127.0.0.1:57091/raw/helix/localhost--local--default/master/footer.md
[hlx] error: Resource not found: /header.plain.html
[hlx] error: Resource not found: /footer.plain.html

[adobe-bot]

🎉 This issue has been resolved in version 4.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀