Add custom rate limit for aiohtpp

[moisses89]

Description

Add a custom client rate limit per second .
The RateLimiter class limit the connections per seconds for the provided rate.
Basically release a number of available connections given by rate each second.

[coveralls]

Pull Request Test Coverage Report for Build 13388974656

Details

• 58 of 62 (93.55%) changed or added relevant lines in 3 files are covered.
• 8 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.004%) to 93.946%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
safe_eth/eth/clients/rate_limiter.py	39	41	95.12%
safe_eth/eth/tests/clients/test_rate_limit.py	16	18	88.89%

Files with Coverage Reduction	New Missed Lines	%
safe_eth/eth/clients/etherscan_client.py	1	85.87%
safe_eth/eth/ethereum_client.py	1	85.21%
safe_eth/eth/tests/clients/test_etherscan_client.py	6	76.47%

Totals
Change from base Build 13372778676:	-0.004%
Covered Lines:	9543
Relevant Lines:	10158

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💛 - Coveralls