Implement CSS-only input toggling, refactor related forms

UX/Translation changes:

- new teams: remove redundant tooltips that don't add meaningful information
  - move general information to table fieldset
- new teams: rename "general" to "custom" access for clarity
- new teams: show labels beside options on mobile

Accessibility:

- semantic form elements allow easier navigation (fieldset, mostly)
- improve better labelling of new teams table
- fix accessibility scan issues
- TODO: the parts that "disable" form elements were not yet touched and
  are not really accessible to screenreaders

Technical:

- replace two JavaScript solutions with one CSS standard
- implement a simpler grid (.simple-grid)
- simplify markup
- remove some webhook settings specific CSS

Testing:

- check more form content for accessibility issues
- but exclude tooltips from the scan :(
- reuse existing form tests from previous PR

web_src/css/modules/grid.css

@@ -1,3 +1,14 @@
+.simple-grid {
+  display: grid;
+  gap: 1em 2em;
+}
+
+@media (min-width: 30em) {
+  .simple-grid.grid-2 {
+    grid-template-columns: repeat(2, 1fr);
+  }
+}
+
 /* based on Fomantic UI grid module, with just the parts extracted that we use. If you find any
    unused rules here after refactoring, please remove them. */