Create a struct to provide build info (#1288)

* Move buildinfo pkg out of internal.

Intended to share this module with verification server.

* Run goimports over modified files.

* Update additional import paths.

* Also remove an unused module.

* Update build.yaml with the new package location.

* Update variable names in buildinfo and have a struct to export these
values.

* Remove unused file.

* Remove unused interface.

* Fix build error.

* Only export a KeyServer variable instead of a struct.

* Revert most of the changes and only add a new public variable.

internal/buildinfo/buildinfo.go

@@ -23,3 +23,19 @@ var (
 	// BuildTag is the git tag from which this build was created.
 	BuildTag string = "unknown"
 )
+
+// info provides the build information about the key server.
+type buildinfo struct{}
+
+// ID returns the build ID.
+func (buildinfo) ID() string {
+	return BuildID
+}
+
+// Tag returns the build tag.
+func (buildinfo) Tag() string {
+	return BuildTag
+}
+
+// KeyServer provides the build information about the key server.
+var KeyServer buildinfo