Network page: show more groups with a button, so the tags stay reachable

[edwh]

For #918.

Summary

• Before: on a network page, the list of groups under the map loaded more groups as you scrolled down. On big networks (Hauts-de-France, Repair Together) the group tags section below kept moving out of reach just as you got to it.
• After: the network page shows a page of groups (25), then a Show more groups (25 of 180) button. The list only grows when you press it, so the tags section stays reachable.
• Why not a fixed-height list that scrolls inside the page: that works on desktop, but on a phone you end up with two scrollable areas on top of each other, and the inner one can be taller than the screen. A button keeps a single scroll on every screen size.
• The groups page keeps scrolling as before. Nothing below its list needs reaching.

Code Quality Review

• GroupsTable gets a showMoreButton option. The network page turns it on (passed through GroupMapAndList); everywhere else is unchanged.

Test Plan

• Jest: with the option on, there's no infinite scroll, the button adds a page, and it disappears once every group is shown. The network page turns it on.
• Full jest suite passes.
• Checked on the preview with Hauts-de-France (245 groups), on a computer and a phone: scrolling no longer grows the list; the button adds 25 groups each time.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Preview: https://restarters-pr-931.fly.dev

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