Thread: pgsql: Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md.

Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md.

These "community health files" provide important information about
the project and will be displayed prominently on the PostgreSQL
GitHub mirror.  For now, they just point to the website, but we may
want to expand on the content in the future.

Reviewed-by: Peter Eisentraut, Alvaro Herrera, Tom Lane
Discussion: https://postgr.es/m/20240417023609.GA3228660%40nathanxps13

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dec9d4acdb7d758c3cbe989ad80cf0367f4e166d

Modified Files
--------------
.github/CODE_OF_CONDUCT.md | 2 ++
.github/CONTRIBUTING.md    | 2 ++
.github/SECURITY.md        | 2 ++
3 files changed, 6 insertions(+)