DOP-4540: Simplify versioned prefix generation

[rayangler]

Stories/Links:

DOP-4540

Current Behavior:

Server docs prod
Atlas docs prod

Staging links to compare with for main branch:
Server docs staging - built with dotcomprd, without path prefix
Server docs staging - built with default dev

Staging Links:

Atlas docs - built with dotcomprd, without path prefix
Server docs - built with dotcomprd, without path prefix
Server docs - built with default dev

Notes:

• Originally part of DOP-4540: Simplify versioned prefix generation regardless of build type #1078. Decided to stick closer to the original scope of the ticket and avoid changing staging prefixes as discussed in some of the comments.
• Removes the need to define a path prefix or have the dev SNOOTY_ENV environment declared in order to see accurate version prefix generation for canonicals and version dropdown URLs. This should make the canonicals and version dropdowns more reflective of behavior on a deployed site.
• Generalizes the version dropdown's generatePrefix util function to be generateVersionedPrefix to semantically decouple it from the version dropdown component. The function should be used specifically for URLs to other versions of the same site project, while withPrefix can continue to be used for URLs for the same/current version of the site.
• Updates tests to reflect expected behavior, especially for canonicals.

README updates

• • This PR introduces changes that should be reflected in the README, and I have made those updates.
• • This PR does not introduce changes that should be reflected in the README

[mmeigs]

Thank you for the comments!! Raymund, this is so clean. Looks great.

[caesarbell]

LGTM