Adding log level configuration from env variable

[italovalcy]

Fix #176

Description of the change

As discussed during the All Hands Meeting, it would be nice if we have means to change the log level of the SDX components for production environment. In production, having the log level hardcoded to DEBUG is not recommended. With this PR, the SDX-LC operator can now set an environment variable called LOG_LEVEL and change this behavior.

For backward compatibility, the LOG_LEVEL defaults to "DEBUG" just as current behavior.

[coveralls]

Pull Request Test Coverage Report for Build 13334264364

Details

• 2 of 5 (40.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 80.936%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sdx_lc/app.py	0	3	0.0%

Totals
Change from base Build 12917532142:	-0.04%
Covered Lines:	1210
Relevant Lines:	1495

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💛 - Coveralls

[YufengXin]

Thanks