Add Gardener v2 parser for switch datatype

[robertodauria]

This PR replaces the current DISCO parser with a new "switch" datatype parser that uses the Sink interface and is compatible with Gardener v2.

• Output column names have been changed to match standard column names and the switch parser design document
• Row size (exported via a Prometheus metric) is calculated according to the datatype size on BQ's Pricing page
• Raw data is re-organized by the parser so that each row contains all the metrics collected by a machine for a given timestamp
• A synthetic unique ID is created for each row by concatenating the machine's hostname and the timestamp (this is required by Gardener to perform deduplication)

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 7102

• 145 of 223 (65.02%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 64.27%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/parser.go	0	2	0.0%
parser/switch.go	145	178	81.46%
schema/switch_schema.go	0	43	0.0%
<!--	Total:	145	223	65.02%	-->

Files with Coverage Reduction	New Missed Lines	%
schema/switch_schema.go	2	0%
<!--	Total:	2		-->

Totals
Change from base Build 7065:	0.1%
Covered Lines:	3916
Relevant Lines:	6093

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💛 - Coveralls