Migration support: "v11" to "v12" (April 2023)

[andreibancioiu]

Here, we describe the main steps for migrating from sdk-core v11 to sdk-core v12.

:bulb: For any questions about the migration, feel free to leave a comment :pray: :bulb:

References:

• Release notes of v12
• SDK-JS cookbook
• SDK-JS examples
• PR(s) that updated the SDK-JS cookbook: https://github.com/multiversx/mx-docs/pull/619
• Main "feat" PR on SDK-JS: https://github.com/multiversx/mx-sdk-js-core/pull/263