Wallet limits: max balance, daily max withdraw, transactions per sec

[callebtc]

New .env variable LNBITS_MAX_WALLET_BALANCE_SAT can limit the maximum balance for each wallet and throw an error if the wallet attempts to create a new invoice.

Example: LNBITS_MAX_WALLET_BALANCE_SAT=1000000

=============UPDATE==============

Legacy banks, exchanges, anything dealing with money have wallet limits, so adding a few more optional wallet limits seems like a good security tool.

Added daily max limit and transactions per second.

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (5edb845) 59.26% compared to head (4cfdcbd) 59.25%.
Report is 1 commits behind head on dev.

Files	Patch %	Lines
lnbits/core/services.py	51.61%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2223      +/-   ##
==========================================
- Coverage   59.26%   59.25%   -0.02%     
==========================================
  Files          60       60              
  Lines        8992     9026      +34     
==========================================
+ Hits         5329     5348      +19     
- Misses       3663     3678      +15     

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[callebtc]

it should be editable on the admin ui aswell

@arcbtc wanted to implement that in this PR

[arcbtc]

LFG!

implemented