pgsql: doc: Add getdatabaseencoding to function docs

doc: Add getdatabaseencoding to function docs

The getdatabaseencoding function was added in bf00bbb0c494 in 1998 but
was never documented. While mostly used in tests, there is no reason
not to document it as this function isn't going anywhere and is already
used in extensions.

Author: Ian Barwick <barwick(at)gmail(dot)com>
Reviewed-by: Thom Brown <thom(at)linux(dot)com>
Reviewed-by: surya poondla <suryapoondla4(at)gmail(dot)com>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Discussion: https://postgr.es/m/CAB8KJ=ij+pznQGub=DkyJuKL=tC=Q=07qSahTyw7TLb0DdNJsg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9fa2c1ebd1757db6032cf81b53f973941be77747

Modified Files
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doc/src/sgml/func/func-string.sgml | 17 +++++++++++++++++
1 file changed, 17 insertions(+)