[+] add graceful fallback for local log parsing

[0xgouda]

• Add privilege check before invoking local parser routine, on failure, fallback to checking remote privileges.
• Update local parsing docs, as we don't necessarily require superuser privileges in local mode; we only need read privilege on the logs dir and its files.
• The check only tests read privilege on the logs dir (i.e, ls), I didn't test all possible directory and file privileges, assuming the default setup, so if a user (postgres or superuser) has read privilege on the logs directory, then he should be able to read all the files.

[coveralls]

Pull Request Test Coverage Report for Build 20658767384

Details

• 9 of 12 (75.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 73.901%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/reaper/logparser.go	9	12	75.0%

Totals
Change from base Build 20632675700:	-0.02%
Covered Lines:	3865
Relevant Lines:	5230

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💛 - Coveralls

[pashagolub]

LGTM!