- Updates API to support renaming TailFS shares.
- Adds a CLI rename subcommand for renaming a share.
- Renames the CLI subcommand 'add' to 'set' to make it clear that
this is an add or update.
- Adds a unit test for TailFS in ipnlocal
Updates tailscale/corp#16827
Signed-off-by: Percy Wegmann <percy@tailscale.com>