New i18n key for meetings in progress

[BigSnicker]

Currently, decidim uses "Join" to mean both "Register" and "Join meeting currently in progress".

This leads to confusion, as "Join" is not used to replace "Sign-Up" or "Register".

The problem is shown below, where "Sign-up" is used before meetings, but we should see "Join" for meetings in progress.

Solution Create a new i18n key to separate the two meanings and allow for different terms to be used.

Ideally,

• decidim.meetings.meetings.show.join = "Sign-up for meeting", "S'inscrire à la réunion"
• decidim.meetings.meetings.show.started = "Join meeting", "Rejoindre la réunion"

[paarals]

this issue can be done with the SLA service, as it's a minor feature @BigSnicker @Laurence-Montgomery @microstudi will take care this week.

[BigSnicker]

A related question came up, while you're looking at i18n terms in meetings, is why we cannot change the term below.

We want this to be clearer, something like "Sign-up or log-in here".