Add transaction specific tests

[ManuGowda]

Description

With the introduction of issue #5571, we no longer have transaction specific util functions. These transaction specific functions will become modules eventually.

As part of the modules(token, keys, etc.) we need to cover transaction specific tests(protocol spec)

Acceptance Criteria

• Update protocol spec related to keys module
• Add tests to cover keys scenario
  • https://github.com/LiskHQ/lisk-sdk/blob/64ec200080be3eef576046fe1586cd07d942ecff/elements/lisk-transactions/test/sign_multi_signature_transaction.spec.ts
  • https://github.com/LiskHQ/lisk-sdk/blob/64ec200080be3eef576046fe1586cd07d942ecff/elements/lisk-transactions/test/register_multisignature_account.spec.ts

Additional Information

Refer PR https://github.com/LiskHQ/lisk-sdk/pull/5591 to get more details about removed tests

[shuse2]

This issue should be addressed in #5607

[shuse2]

This util function is tested in #5591 and the missing test is addressed in #5607