update credential image

[mtuchi]

Short Description

Update lightning_credentials_overview.webp which is used on Manage Credentials page

Closes #690

AI Usage

Please disclose how you've used AI in this work (it's cool, we just want to know!):

• [ ] Code generation (copilot but not intellisense)
• [ ] Learning or fact checking
• [ ] Strategy / design
• [ ] Optimisation / refactoring
• [ ] Translation / spellchecking / doc gen
• [ ] Other
• [x] I have not used AI

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[mtuchi]

@theroinaochieng i couldn't test it locally, Try to test on your end before approving this PR

yarn generate-adaptors
yarn generate-library
yarn build
yarn serve

[mtuchi]

@theroinaochieng is this not done ? what's pending?