Available Balance Mismatch Due to Locked Storage

[AlexKushnir1]

The available account balance currently does not match the default balance because a part of the total funds is automatically locked for storage usage. As a result, the computed available balance is less than the expected default value
This confusion appears since users expect the available balance to initially equal the default balance.
I catch this in next test, where preveously was test.near account with pre-locked amount of Near:
https://github.com/near/near-api-js/blob/7fe82aab022525f6ecbce6f270070f6760b0979b/e2e/tests/accounts.test.ts#L37-L40

I suggest to add locked_balance with default zero value and set to sandbox account with some amount.

I could work on it!
cc: @akorchyn @frol