Allow explicit empty string for alt (for accessibility purposes)

[andeng1106]

Is your feature request related to a problem? Please describe.

• The Image block and Card block has an <alt> tag. Upon trying to add an empty alt via "Edit as HTML" or Code Editor and saving the page, the <alt> tag gets removed since our blocks currently doesn't allow explicit empty string for alt, compared to how the native Image block works.
• Sandbox test page: https://gambitsandbox.instawp.xyz/andrea/image-alt-text-test/
• Notion page link: https://www.notion.so/Vadim-150584f29f4c805ea326ce3b07816b43

Describe the solution you'd like

• Allow explicit empty string for alt (for accessibility purposes), similar to the native Image block

Screen.Recording.2024-12-02.at.3.mp4

Describe alternatives you've considered
N/A