[enriched/github] Add demography study

[zhquan]

This code allows executing demography study.

Test added accordingly.

Signed-off-by: Quan Zhou quan@bitergia.com

[coveralls]

Pull Request Test Coverage Report for Build 863807671

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 64 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 82.295%

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Files with Coverage Reduction	New Missed Lines	%
/home/runner/work/grimoirelab-elk/grimoirelab-elk/grimoire_elk/enriched/github.py	64	75.79%
<!--	Total:	64		-->

Totals
Change from base Build 835557357:	0.005%
Covered Lines:	8622
Relevant Lines:	10477

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💛 - Coveralls

[ajaragz]

Changes seem fine. To test them, I've created a demography study for Github

[github]
...
studies = [enrich_demography:github]

...

[enrich_demography:github]

These required settings should probably be also added to the Github section in the Mordred docs https://github.com/chaoss/grimoirelab-sirmordred#github-

After running mordred, the documents in the Github issue index now have the demography_max_date and demography_max_date fields-

LGTM