feat: handle custom ios identifiers

[achorein]

Summary

"plugins": [
      [
        "expo-share-intent",
        {
          // default `group.${appIdentifier}`
          "iosAppGroupIdentifier": "group.expo.modules.exposhareintent.custom",
          // default "ShareExtension"
          "iosShareExtensionName": "My Super Share Extension",
        }
      ],
    ],

Todo

• Allow to set Application Group Identifier for share extension
• Allow to change Extension Bundle Identifier
• Update README.md

Issue

Fixes #94
Fixes #88