Include Flashbots logo to dashboard charts

[elenahoo]

Issue raised by @tkstanczak. On our transparency dashboard each chart needs to either have:
Source: transparency.flashbots.net in gray
OR a watermark flashbots logo and flashbots text behind each chart
OR a flashbots logo and text in the corner of each chart

Charts are often screenshot and used in presentations and presenters not always attribute source in a desirable way (or not attribute at all). Adding a watermark and logo increases flashbots awareness, provides free marketing on multiple quality conferences.