Decide a better way to pull in the stuff that’s currently Git submodules

[lawrence-forooghian]

The external/common and external/sdk-test-proxy directories are currently Git submodules. This means that when a user installs the SDKs using Swift Package Manager it will clone these repositories. However, this repositories are only development dependencies, and it doesn't seem like a good idea to impose this overhead on users.

Perhaps it would be better to have a script that clones these repos for development instead.

We should then update the guidance in https://github.com/ably/ably-asset-tracking-common/tree/e5cd278a910a287a04a91e4b320a3079287fc31f#usage-in-downstream-repositories.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-3528