docs(knapsack): fix icon rendering bug and add icon lockup

[bsahitya]

Description

Issues in knapsack fixed in this PR:
Icons are not rendering in knapsack docs.
Code editor, notebook cell docs do not show up in the sidebar.

New additions:
Add docs for Icon lockup component

What's included?

• Update knapsack metadata to fix icon bug.
• Add notebook cell, code editor back to the docs site sidebar
• Add docs for the new icon lockup component.

Test Steps

• npx nx run knapsack:serve
• then check icon, icon button and icon button toggle components
• finally verify if icons are displayed in these components

General Tests for Every PR

• npm run start still works.
• npm run lint passes.
• npm run stylelint passes.
• npm test passes and code coverage is not lower.
• npm run build still works.

Screenshots or link to StackBlitz/Plunker