Add NGINX redirect rules for erroneous API pages and test configuration

[RayOffiah]

Added rules to trap and redirect the pages for API Enumerations and Structures.

[osfameron]

doesn't seem to work, e.g

• 404 https://infratest.docs-test.couchbase.com/mobile/2.8.4/couchbase-lite-swift/Enumerations.html
• 404 https://infratest.docs-test.couchbase.com/mobile/2.8.4/couchbase-lite-swift/Structures.html

Looking at our rewrites, we don't use ~* at all... I wonder if we could use the approach used elsewhere, something like:

location ^~ /mobile/ {
    rewrite ^/mobile/([^/]+)/(couchbase-lite-swift)/Enumerations.html$ /mobile/$1/$2/Enums.html redirect; 
    rewrite ^/mobile/([^/]+)/(couchbase-lite-swift)/Structures.html$ /mobile/$1/$2/Structs.html redirect; 
}

(Not tested 🙈)

[RayOffiah]

Okay, changed it target the mobile section.

[RayOffiah]

Works locally, but so did the last attempt.

[RayOffiah]

It also suggested moving the section further up in the config so that it gets matched earlier on, but let's try this first.