feat(www): add sidebar for mobile view and make home page responsive

[DuskoPeric]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Home page and side menu are not responsive for small screens

Closes #4807

What is the new behavior?

Home page and side menu are responsive for small screens

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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[timdeschryver]

This looks fine on the homepage, but on other pages the new design cuts of the title, e.g. at https://deploy-preview-4813--ngrx-site-v19.netlify.app/guide/store/why

Do you think we can fix this as well?

[markostanimirovic]

@timdeschryver

I opened issues for other pages: #4816 #4817