Joining Public Communities from Community site: update Groups API from V3 to V5

[SathyaJayabal]

When a member joins a public community from the community site, the V3 groups api call is used. This must be updated to V5 groups api call.

cc @lakshmiathreya

[SathyaJayabal]

@sushilshinde in production, not able to join the group using the Join button



cc @lakshmiathreya

[lakshmiathreya]

@dushyantb @sushilshinde @SathyaJayabal - Added this Issue to v5 Integration since it was planned for inclusion at this milestone.

[Oanh-and-only-Oanh]

Moving this to lowest priority. The public subcommunities are not something we're highlighting or focusing on.