Tezlink/Kernel: Add functions in account_storage to handle manager and account initialization

Previous MR

!17730 (merged)

Next MR

!17684 (merged)

What

Add functions in Tezlink account_storage to handle manager fields and account initialization.

Why

Manager fields are needed for operation as this is the field where we'll retrieve the public key for a tz account. The exist function will be useful for the validity of a Tezlink operation, to verify if an account exist (we check as this is the field that represent activity on an account). An init function was also introduced to init all necessary fields of an account

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR