pgsql: Replace search.cpan.org with metacpan.org

Replace search.cpan.org with metacpan.org

search.cpan.org has been EOL'd, with metacpan.org being the official
replacement to which URLs now redirect.  Update links to match the new
URL. Also update links to CPAN to use https as it will redirect from
http.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/B74C0219-6BA9-46E1-A524-5B9E8CD3BDB3@yesql.se

Branch
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REL9_3_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6acb4e89fe472e74bcbb3d3b997cccef6c026be9

Modified Files
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doc/src/sgml/acronyms.sgml          | 2 +-
doc/src/sgml/external-projects.sgml | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)