Asn annotator - first phase

[zkauker]

To make sure that I won't impact the current codebase I decided that in the first phase I copy-paste the implementations which are needed but cannot be reused as it is right now (package private functions for building the IPNode list and then doing a binary search on that). I'm going to continue with externalizing this logic.

TODOs:

• eliminate the code duplications with refactor (will be a separate PR)
• the unit tests are built on the contents of mlab-sandbox environment -> should move the necessary files to mlab-test's downloader-mlab-test bucket to make sure that the unit tests will work with the CI/CD tool
• reduce the memory pressure by merging the overlapping IP ranges with the same ASNs

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 1998

• 7 of 38 (18.42%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-1.2%) to 52.096%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
loader/loader.go	0	4	0.0%
geoloader/geoloader_asn.go	0	27	0.0%
<!--	Total:	7	38	18.42%	-->

Files with Coverage Reduction	New Missed Lines	%
api/v2/api-v2.go	1	75.31%
<!--	Total:	1		-->

Totals
Change from base Build 1995:	-1.2%
Covered Lines:	783
Relevant Lines:	1503

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💛 - Coveralls