Add `OAUTHBEARER` support

[coveralls]

Pull Request Test Coverage Report for Build 9146872460

Details

• 10 of 10 (100.0%) changed or added relevant lines in 2 files are covered.
• 29 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 92.22%

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Files with Coverage Reduction	New Missed Lines	%
imap-codec/src/auth.rs	5	93.51%
imap-types/src/auth.rs	24	51.28%
<!--	Total:	29		-->

Totals
Change from base Build 9146763732:	-0.2%
Covered Lines:	9993
Relevant Lines:	10836

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💛 - Coveralls