fix(frontend): send invitation clearer (#3090)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/app/studio/[brainId]/BrainManagementTabs/components/PeopleTab/PeopleTab.tsx

@@ -52,10 +52,14 @@ export const PeopleTab = ({ brainId }: ShareBrainModalProps): JSX.Element => {
             ></QuivrButton>
             <QuivrButton
               isLoading={sendingInvitation}
-              disabled={roleAssignations.length === 0}
-              label="Invite"
+              disabled={
+                !roleAssignations.some(
+                  (roleAssignation) => roleAssignation.email !== ""
+                )
+              }
+              label="Send invitation"
               color="primary"
-              iconName="share"
+              iconName="invite"
               onClick={inviteUsers}
             ></QuivrButton>
           </div>

frontend/lib/helpers/iconList.ts

@@ -48,6 +48,7 @@ import { HiBuildingOffice } from "react-icons/hi2";
 import {
   IoIosAdd,
   IoIosRadio,
+  IoIosSend,
   IoMdClose,
   IoMdLogOut,
   IoMdSettings,
@@ -156,6 +157,7 @@ export const iconList: { [name: string]: IconType } = {
   home: IoHomeOutline,
   html: BsFiletypeHtml,
   info: FaInfo,
+  invite: IoIosSend,
   ipynb: BsFiletypePy,
   key: MdOutlineVpnKey,
   link: MdLink,