Rewritten Getting Started guide

[mhmohona]

Description:

• Renamed current "KEDA Documentation" heading to "Getting Started".
• In Deploying KEDA page, explained each installation method.
• Added "Hello KEDA" page based on https://github.com/kedacore/sample-hello-world-azure-functions.

Checklist

• Commits are signed with Developer Certificate of Origin (DCO)

Fixes #1364

[github-actions]

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[netlify]

❌ Deploy Preview for keda failed.

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🔨 Latest commit	3897cc0
🔍 Latest deploy log	https://app.netlify.com/sites/keda/deploys/668bd24050af240008f2f9b5

[mhmohona]

I am confused how shall I set the weight for the new page I created named "Hello KEDA".

[tomkerkhove]

@mhmohona Can you please fix the build issue?

[tomkerkhove]

Can you fix the DCO issues please? You can learn more in our contribution guide.