Get rid of using seeds in VestingAddin instructions

[s-medvedev]

Problem: seeds-field used only to enable the creation of several vesting records for one owner. But it makes a problem for UI to find the correct seeds-value from known VestingRecord. To do this, you need to ask the user or look at the history to find a transaction to create.

Suggested solution: Use vesting_token_account as a seed to generate PDA for VestingRecord.

Rationale: This field already passed through instructions. Moreover, the internal implementation of vesting allows only a one-to-one link between VestingRecord and its vesting token account.
In this case, UI is available to find all VestingRecords using get_program_accounts method and then find the correct token_vesting_account.

┆Issue is synchronized with this Jira Task by Unito