Rewrite getPublicKey function

[payvint]

Problem:

This function is converting public key manually, it would be good to use already created solution from ethers/web3 libraries.
Because it affects stability of running tests and can fail tests.

Investigation described here #1341

Solution:

Find function which will fit our tests:

• Input can be a Wallet/Signer from ethers library or private key
• Return array of two 32 bytes hex string starts with "0x"