[#1235] add /transaction/watch endpoint & background tx status process

[jankun4]

List of changes

Added

• /transaction/watch/ websocket endpoint
• background transaction status process, that looks for watched transactions and sends {"status": "confirmed"} via websocket when transaction is found. This process works in iterations, once per 20 seconds.

IMPORTANT!!!

each /transaction/watch request stores a UUID in Redis in database number 1 (not 0)
this redis store, together with in-memory uuid to WebSocket.Connection map is used to notify user, that transaction of interest is confirmed.

Checklist

• related issue
• My changes generate no new warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the changelog
• I have added tests that prove my fix is effective or that my feature works

[MSzalowski]

Could you please verify&fix if possible backend actions?

[MSzalowski]

Notes:

• To validate acking the message
• To validate timeout when listening to the non-existing txhash

CC @jankun4