Updates ruby version 2.5 to 3.0

Updates ruby version 2.5 to the latest (3.0 or 3.0.1) since Ruby 2.5 was just EOL'ed on 2021-03-31.

specs

• FOSS specs !59230 (merged)
• EE specs !59229 (merged)

docs

• docs !59232 (merged)

CI templates

• Dockerfile templates !59345 (merged)

Configuration of GitLab.com gitlab.com

Out of scope from Community contribution since these are NOT disclosed even for Core Team