website: Legacy Releases -> Maintenance Releases

[ziaee]

Summary

Legacy is a bad name that forces the reader to draw from context.
It makes them say "I could figure out what this means" instead of
"I understand what this means". Maintenance Releases tells the
reader what they want to know, improving the clarity of our information
ecosystem.

[ziaee]

align "where" naming convention with "release information" naming convention.

[ziaee]

release information: s/maintenance releases are for existing users/maintenance releases are for existing deployments/ because... it's the deployment that is selected for the conservative update strategy, not the user.