[feature/remove-intents-extension] Remove Extension Build Flag (Intents)

[hosy]

Description

This PR adds a possibility to remove app extensions from a IPA build.

For the related issue it is needed to remove the ownCloud Intents extension to remove Shortcuts and Siri support from the ownCloud app.

Related Issue

https://github.com/owncloud/enterprise/issues/6112

Motivation and Context

How Has This Been Tested?

Add this key/value pair to the Branding.plist file and build the app via fastlane:

	<key>build.flags</key>
	<string>REMOVE_EXTENSION_INTENTS</string>

fastlane release_on_appstore create_release_notes:false create_screenshots:false build_regular_app:true build_emm_app:false build_owncloud_online_app:false deliver:false

This will execute the new shell script removeExtension.sh with the following parameter:

../removeExtension.sh "../ownCloud-regular-12.0.3-feature_remove-intents-extension-app-store-xy.ipa" "ownCloud Intents"

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• Added an issue with details about all relevant changes in the iOS documentation repository.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• Added changelog files for the fixed issues in folder changelog/unreleased

[michaelstingl]

Update /doc/BUILD_CUSTOMIZATION.md ?