[dmt] add docs linter

[RottenRat]

New documentation linter (pkg/linters/docs):

The readme rule checks for the presence of README.md in the module.
The bilingual rule requires documentation in two languages: README.md and README_RU.md (empty files are also caught as an error).
Cyrillic-in-English rule - searches for Cyrillic characters in English .md files (without the _RU suffix).

Configuration:

Added documentation sections to global.Linters and LintersSettings with support for impact, exclude-rules (lists of modules/files/directories), and bilingual.disable. Merge impacts have been implemented. The rules and a YAML example are described in pkg/linters/docs/README.md.

Metrics and minor fixes:

metrics.SetLinterWarningsMetrics now accepts *global.Global.

Test data:

Example modules have been added: bad-cyrillic, bad-readme, good-module, as well as cases in testdata/docs-test and test-config.yaml to test the new rules.

Now dmt can automatically check that the module has a README, that the documentation is bilingual, and that there is no Cyrillic in English files. All of this is configured via linters-settings.documentation and included in the metrics.

Tests:

Add Minimocs

##Manual tests
good-module: OK

bad-readme:

🐒 [readme (#documentation)]
     Message:      README.md file is missing in module
     Module:       bad-readme
     FilePath:     README.md

bad-cyrillic:

🐒 [bilingual (#documentation)]
     Message:      README_RU.md file is missing - documentation should be available in both languages
     Module:       bad-cyrillic
     FilePath:     README_RU.md

🐒 [cyrillic-in-english (#documentation)]
     Message:      English documentation contains cyrillic characters
     Module:       bad-cyrillic
     Value:        Line 3: This module has кириллические символы in English documentation.
                   ----------------^^^^^^^^^^^^^-^^^^^^^
                   Line 5: ## Описание
                   ---^^^^^^^^
                   Line 7: This section contains русский текст mixed with English.

all modules:

time=... level=INFO msg="Run linters for `good-module` module"
time=... level=INFO msg="Run linters for `bad-cyrillic` module"
time=... level=INFO msg="Run linters for `bad-readme` module"

🐒 [bilingual (#documentation)]
     Message:      README_RU.md file is missing - documentation should be available in both languages
     Module:       bad-cyrillic
     FilePath:     README_RU.md

🐒 [cyrillic-in-english (#documentation)]
     Message:      English documentation contains cyrillic characters
     Module:       bad-cyrillic
     Value:        Line 3: This module has кириллические символы in English documentation.
                   ----------------^^^^^^^^^^^^^-^^^^^^^
                   Line 5: ## Описание
                   ---^^^^^^^^