feat: expose SetLogLevel in cli

[iwpnd]

Allow user to set a desired log level on startup with --log-level Level.
Omitting the flag results in the default INFO

Hey 👋

I got to one of my proposition from #831.
As options I went for the log levels that @gdey has already set - all I did is exposing SetLogLevel in the root.

Let me know if you prefer those levels for the flag instead:

very-verbose = TRACE
verbose = DEBUG
default = INFO
quiet = WARN
silent = ERROR

Where do the docs live actually? 🤔

[coveralls]

Pull Request Test Coverage Report for Build 62aaf7955-PR-834

• 3 of 26 (11.54%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.06%) to 45.141%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/tegola/cmd/root.go	3	26	11.54%

Totals
Change from base Build ac85a37e4:	-0.06%
Covered Lines:	5486
Relevant Lines:	12153

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💛 - Coveralls

[ARolek]

This looks fine to me. Since tegola is not using the centralized log package throughout the codebase yet, should we add a note to the flag to say it's only partially adopted at this point?

[iwpnd]

understood. I added the options and labelled the flag as a work in progress.

[iwpnd]

@gdey since this is actually your work and not mine, are you okay with this?

[ARolek]

closed in e593b4f