docs: CHARTS-6059 Extract common text from SDK guides

[lilyh4]

Summary

• Our SDK examples share a lot of common text in their README.md files
• Common partial files have been added to a new directory examples/docs
• Used npm package markdown-include to support building our README files with other Markdown files
  • With each outputted README.md (one per SDK example) there now needs to be a new markdown.json file which specifies the build file for it
    • These build files are located in examples/.md-config
  • Until we set up an action, compilation is manual (see below)
• With this approach, future text changes should only be made to the configuration files or the partial docs

Script to compile all SDK guide README files:

for i in examples/charts/* examples/dashboard/*;
  do ./node_modules/markdown-include/bin/cli.js "${i}"/markdown.json;
done;

Updated file tree

charts-embed-sdk/examples
├── .md-config
│   ├── chart
|   |   ├── authenticated-custom-jwt.md     
|   |   └── ...other md config files            
|   └── dashboard
│       └── ...other md config files        
├── charts
│   ├── authenticated-custom-jwt
|   |   ├── assets
|   |   ├── src     
|   |   ├── app.js  
|   |   ├── index.html 
|   |   ├── markdown.json       
|   |   ├── package.json    
|   |   ├── package.json    
|   |   └── package-lock.json 
|   └── ...other examples   
├── dashboard
|   └── ...other examples   
├── docs
│   ├── chart
|   |   └── ...partial md files
|   ├── dashboard
|   |   └── ...partial md files
|   └── ...partial md files
└── README.md