Add guidance for package maintenance

Cover topics like:

- Use the module template
- Follow SemVer
- Changelog maintenance
- Testing prerelease builds locally and on CI
- e.g. yarn link or file:// for local, preview builds for CI
- dependencies vs peerDependencies vs devDependencies

Notes:
This message was on Slack and should be included in the guidelines in some way:
PSA: There are two primary ways that we communicate changes we've make to our NPM packages to consumers. Changelogs are one of them, but we also use versions as a coarse indicator as well. I have seen several instances over time where a version for a released package was bumped in a way that either oversells or undersells the changes inside of that release. For instance:

- Bumping the minor part of a version if new functionality was not being added, when only the patch should have been bumped
- Bumping only the patch part of a version when new functionality was added, when the minor should have been bumped
- Not bumping the major part of a version when breaking changes are introduced

As a reminder, we use [SemVer](https://semver.org/) to assign new versions for packages. I would recommend everyone read this when they get a chance, especially the "Why Use" section and the FAQ.

Start by reviewing the existing contributor documentation and the linked SemVer guidance, then identify where package-maintenance guidance belongs. Cover the module template, versioning, changelogs, prerelease testing, dependency types, and the local and CI workflows listed in the issue. Done means these topics are documented clearly for package contributors.

Written by the indexing model from the issue text.