[8.x] Change ca certificate path config key. (#195233) (#195467)

# Backport

This will backport the following commits from `main` to `8.x`:
- [Change ca certificate path config key.
(#195233)](https://github.com/elastic/kibana/pull/195233)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

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Co-authored-by: Ersin Erdal <92688503+ersin-erdal@users.noreply.github.com>

x-pack/plugins/actions/server/config.ts

@@ -147,7 +147,7 @@ export const configSchema = schema.object({
   ),
   usage: schema.maybe(
     schema.object({
-      cert: schema.maybe(
+      ca: schema.maybe(
         schema.object({
           path: schema.string(),
         })