Allows tagging of runbooks

[whitdog47]

This PR allows users to tag runbooks. Note that desired tag types must have the "Document" discoverability checked.

[wssheldon]

              <v-col cols="12">
                <tag-picker
                  label="Tags"
                  v-model="tags"
                  :project="project"
                  model="document"
                  :model-id="id"
                  show-copy
                />
              </v-col>

Does it only show valid elements (e.g. Note that desired tag types must have the "Document" discoverability checked)? -- Best case, I think, we only show valid elements, and there's an info tooltip that says what elements are shown.

[whitdog47]

@wssheldon yes, the model prop here tells the tag picker which tag type discoverability model to use.