Add application date to candidate list on validator teams page

[martien-176]

Is your feature request related to a problem? Please describe.

https://tasks.hotosm.org/manage/teams/7
https://tasks.hotosm.org/manage/teams/1

Most of the time it is not possible to endorse a promising validator candidate immediately. The actual endorsement happens some time later. Often a backlog builds up in the mean time.
Knowing when a candidate applied is important to assess them properly. Therefore, having the date of application is important for the endorsement process.

Describe the solution you'd like

Add the date of the application request to every candidate in the list.

Describe alternatives you've considered

• It shouldn't necessarily be in the list itself. A popup would also do.
• A way to download the list as a CSV file would be great. Including the date.

Additional context

n/a

**Add any other context or screenshots about the feature request here.

n/a

[ramyaragupathy]

@prabinoid - do you know if we track user's request to join a team? Specifically, capturing when the request was sent. I don't remember this information being tracked in the backend.

cc @manjitapandey @royallsilwallz