Update snackbar message on "Discover Existing" functionality

[ll5zh]

Is your feature request related to a problem? Please describe.
Upon syncing Dockstore entries using "Discover Existing", the snackbar message reads: "Adding user to existing workflows and tools on Dockstore succeeded/failed". This might be misleading if you had clicked "Discover Existing Notebooks" from the my-notebooks page, because there is no mention of notebooks.

Describe the solution you'd like
Possible ways to reword:

• "Adding user to existing workflows, tools, and notebooks on Dockstore"
• "Adding user to existing entries on Dockstore"

Describe alternatives you've considered

• Keep the message as is
• Customize the message based on what entry page the user is on; for example, "Adding user to existing notebooks on Dockstore" if on my-notebooks. This is probably more misleading though, as clicking "Discover Existing" does sync entries of all types

Additional context

┆Issue is synchronized with this Jira Story
┆Fix Versions: Dockstore 1.17
┆Issue Number: DOCK-2522
┆Sprint: Backlog
┆Issue Type: Story