Add 'pmid' to the default interwiki list, and update 'rfc'

Add 'pmid' to the default interwiki list, and update 'rfc'

As an alternative to using magic links, PMID was added to the default
interwiki list.

RFC already existed, but the URL in the default list was pointing to
rfc-editor.org, not the tools.ietf.org view like the RFC magic link or
Wikimedia interwiki map are.

Updating the default lists in maintenance/interwiki* only affects new
installations, so a post-database update maintenance script adds and
updates the two interwiki prefixes.

Bug: T147536
Change-Id: I5a2c2c9b0f989da62a4395c9516d880c7d923444