CS Handbook page updates

[simfish85]

Changes

Please describe.

1. Updated billing page to document process for annual + overage
2. Fixed YC Deal info
3. Updated target customer profile
4. Added our current processes to sales ops page

Add screenshots or screen recordings for visual / UI-focused changes.

Checklist

• [x] Titles are in sentence case
• [x] Feature names are in title case
• [x] Words are spelled using American English
• [x] I have checked out our style guide

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