feat: update to include approval flow for paymaster onboarding

[dutterbutter]

What :computer:

• Adds approval paymaster flow guide
• Makes small edits / fixes

Why :hand:

• Distinction between approval flow and general flow paymasters

Evidence :camera:

Include screenshots, screen recordings, or console output here demonstrating that your changes work as intended

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit d14e941):

https://zksync-docs-staging-5eb09--pr17-db-approval-paymaste-3ggvotei.web.app

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