[TASK] Prepare for package renaming in next major version

Repository is already renamed, and with the next major
version 5.x the composer package name and extension key
are renamed. This change prepares toward this renaming
by adding corresponding conflict to `composer.json` and
`ext_emconf.php`.

Additionally, basic version branch preparation is done.

Used command(s):

```shell
git checkout main && git fetch --all && git pull --rebase && git checkout -b 4
cat composer.json | jq '.conflict."webvision/deepltranslate-core"="*"' --indent 4 | sponge composer.json
composer config --unset extra.branch-alias.dev-main
composer config extra.branch-alias.dev-4 "4.x.x-dev"
```

composer.json

@@ -39,7 +39,8 @@
 		"source": "https://github.com/web-vision/wv_deepltranslate"
 	},
 	"conflict": {
-		"studiomitte/recordlist-thumbnail": "*"
+		"studiomitte/recordlist-thumbnail": "*",
+		"webvision/deepltranslate-core": "*"
 	},
 	"config": {
 		"vendor-dir": ".Build/vendor",
@@ -62,7 +63,7 @@
 			"app-dir": ".Build"
 		},
 		"branch-alias": {
-			"dev-main": "4.x.x-dev"
+			"dev-4": "4.x.x-dev"
 		}
 	},
 	"require": {

ext_emconf.php

@@ -26,6 +26,7 @@
         ],
         'conflicts' => [
             'recordlist_thumbnail' => '*',
+            'deepltranslate_core' => '*',
         ],
         'suggests' => [],
     ],