Documentation updates - Githubissues

This change includes the following:

Adds a link to the Enum Behavior topic from the Editions Features topic
Updates the "Use Well-Known Types and Common Types" section of the Dos and Don'ts topic to remove redundancy
Adds information about creating plugins to the "Other Languages" topic
Updates the Versions Supported topic for the v27 release

protocolbuffers / protocolbuffers.github.io