Replace EOTK repository URL with Onionspray's

Tasks

• Update EOTK link at https://community.torproject.org/onion-services/, pointing to https://gitlab.torproject.org/tpo/onion-services/eotk.
• Update the repository link in other relevant pages.
• Replace, again, this time with Onionspray.

Time estimation

• Complexity: very small (0.5 day)
• Uncertainty: low (x1.1)
• Reference (adapted)

/cc @gus