[ImgBot] Optimize images

*Total -- 1,252.30kb -> 997.65kb (20.33%)

/mails/pre_release_week_1/strategies.png -- 64.84kb -> 40.11kb (38.14%)
/mails/pre_release_week_1/rewards.png -- 116.21kb -> 85.00kb (26.86%)
/mails/pre_release_week_1/learn.png -- 192.95kb -> 141.48kb (26.67%)
/mails/pre_release_week_1/app-dashboard.png -- 43.09kb -> 32.13kb (25.43%)
/mails/pre_release_week_1/app-explorer.png -- 181.17kb -> 136.83kb (24.47%)
/mails/product_hunt/octobot-2.0.0-preview-dark.png -- 109.57kb -> 88.82kb (18.94%)
/mails/product_hunt/octobot-2.0.0-preview.png -- 107.90kb -> 87.66kb (18.75%)
/mails/pre_release_week_1/news.png -- 436.57kb -> 385.62kb (11.67%)

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