Cache collections with new CacheablePathsProcessor

[jimchamp]

Closes #9058

Creates new CacheablePathsProcessor that can be used to cache Infogami pages without overriding the default Infogami handler for such pages.

This processor attempts to fetch pages from cache when the following are true:

1. The request is a GET
2. The request is not specially encoded data (json, yml, etc.)
3. The request's path matches one of the patterns in the paths_and_expiries dictionary
4. debug is not in the request's query string
5. The requested page's mode is view

The processor has been set up to cache/collections and /collections/{collection_identifier} pages.

Technical

Cache keys will take the form:
{web.ctx.path}.{web.ctx.lang}{query_string}

...where query_string is either an empty string or an ordered query string (e.g. ?a=1&b=1&c=1)

Adding a new path pattern and expiry time to paths_and_expiries will enable caching for pages matching to path pattern.

Testing

1. Deploy this branch to a testing environment
2. Navigate to the /collections page
3. On page load, refresh the page

The load time on refresh should be noticeably faster than the initial page load.

Screenshot

Stakeholders

@mekarpeles

[jimchamp]

Reviewer: Is it okay to use this caching_prethread?

I more or less re-implemented the homepage caching in this new processor, which uses caching_prethread.

[jimchamp]

Reviewer: Please check the order of the conditionals that return handler().

My goal is to order these such that we exit this method as quickly as possible if the page isn't being cached by this processor.

[mekarpeles]

In addition to languages, print-disabled patron status and potentially safe-for-work mode may be useful to consider here.

It may be nice to codify what these are e.g. language, region, safe for work, print disabled, etc.

[mekarpeles]

At minimum, cache should take into consideration lang and printdisabled (in he future sfw

[jimchamp]

Caching localized pages was already in place (we both missed that during our quick review). Have added additional caching for print-disabled page requests, and have included commented-out code for sfw.