feat: branch sdk integration

[saeedbashir]

This PR adds the integration of the Branch SDK. The Branch SDK will be used for deep links.

Config

BRANCH:
    ENABLED: true
    KEY: 'branch_key'
    URI_SCHEM: 'URI_SCHEME'  #optional, if not provided, the product identifier will be used as URI scheme
    DEEPLINK_PREFIX: 'prefix'  #optional, if not provided, `edx` will be used as prefix for deeplink configurations

[rnr]

Maybe this should be moved to whitelabel script too? Thoughts?

[saeedbashir]

We/community can add this capability to the whitelabel script to modify the entitlements if needed. But I think we can use edx as a placeholder in the codebase. Thoughts?

[volodymyr-chekyrta]

Please let's move it to the config file if possible.
It will be much clearer for the community to configure everything from the configuration file.

[saeedbashir]

@volodymyr-chekyrta @rnr I've also made the Associated Domains configurable and it will be added when Branch is enabled and will also configure values as per DEEPLINK_PREFIX

[saeedbashir]

@volodymyr-chekyrta @rnr I've added the default values as well. The scene of info.plist and entitlements is different. The info.plist is baked into the IPA file so the updated file is directly modified inside the IPA, hence to trackable change is there.

But in the case of entitlements, the changes are directly applied to the entitlements file and they are git trackable if there will be any change because of prefix. That's why I've added edx as a placeholder value so that for edX and openedX the change will not appear in the changeset. Otherwise, we have to remove the changes of this file before committing any changes and we can't even add it to git ignore because in the future more entitlements can be added.

[saeedbashir]

@volodymyr-chekyrta Could you please spare some time and review this PR.

[volodymyr-chekyrta]

LGTM 👍