Consolidate 301 redirects from legacy URL structures

[jonoaldersonwp]

Requests to legacy URL structures undergo multiple 301 redirects, which represents an SEO and performance issue.

E.g., requests to ​http://www.wordpress.org/plugins/knews-contact-form-7-glue undergo the following:

301 to ​https://www.wordpress.org/plugins/knews-contact-form-7-glue (http > https)
301 to ​https://wordpress.org/plugins/knews-contact-form-7-glue (www > non-www)
301 to ​https://wordpress.org/plugins/knews-contact-form-7-glue/ (force trailing slash)

We should consolidate this into as few 'hops' as possible.

• The http > https and removal of www should be consolidated into a single rule.
• Where possible elsewhere, the trailing slash rule should also be integrated into the same step.
• In this case, the addition of the trailing slash should be integrated into the same rule, based on the path beginning with /plugins/ , and the omission of a file extension at the end.

[jonoaldersonwp]

See also, #4075

[dd32]

Unfortunately most of this is in the too-hard basket without rewriting how WordPress.org is setup, as most of these functions are performed by different levels of server infrastructure (LB redirects, Web node redirects, more LB redirects, and finally some PHP redirects).

If this isn't strictly required but a rather "nice to do", please close this as it'll never be implemented otherwise (And if it is implemented, it'll only be to reduce some of the hops, unlikely to reduce it to 1)