Add earn endpoints

[PastorJordi]

Hi there! Congrats for this library. Because the latest new is that this is not maintained I am dropping a PR which

1. Removes methods to interact with /Staking endpoints which are no longer available since 1st or March, 2024. Namely:

• stake_asset
• unstake_asset
• get_stakeable_assets
• get_pending_staking_transactions
• get_staking_transactions

2. Implements methods to interact with earn endpoints:

• get_earn_strategies for Earn/Strategies
• get_earn_allocations for Earn/Allocations
• get_allocate_status for Earn/AllocateStatus
• get_deallocate_status for Earn/DeallocateStatus
• allocate_earn_funds for Earn/Allocate
• deallocate_earn_funds for Earn/Deallocate

Hence resolves #83

3. Other minor changes:
   • Avoids pandas' FutureWarning when setting index.freq in get_ohlc_data()
   • If there are no orders retrieved by get_open_orders(), even though it still has the behavior .empty == True , now the returned pd.DataFrame has the expected columns defined. IMO, this helps reducing boilerplate if not df.empty: statements in the applications built upon this library

Even though I am bad at styling without linters, I've tried to stick to the original code-style. Feel free to raise comments, cherry-pick or whatever you feel

[dominiktraxl]

Thank you for the PR.

I'm gonna trust you on this one and let the crowd judge. I don't even have an account with Kraken anymore and therefore can't test it.

[PastorJordi]

I did some minimal testing on my end. That's how I discovered the easter egg of hide_zero_allocations param in Earn/Allocations expecting a string literal "true" or "false". In any case, all pykrakenapi users should test these new methods before putting them into production.