Add ability to not cache-bust a particular URL in a check directive

[mcbridem]

Some URLs behave differently when a cache-buster—a query string—is appended. Setting aside whether it's reasonable for a Web server or Web application to behave differently if, for example, /?_=1234 is requested instead of /, URLs observed in the wild do sometimes differentiate, making testing difficult.

Would it make sense to add a no_cachebust: true or similar flag to check directives? This feels kind of hokey and it would be an inverted label. On the other hand, it would somewhat neatly complement the --no-cachebust command-line argument. By default we cache-bust all URLs and transform them if a non-live level is specified. Maybe a more generic leave_this_url_alone: true (or exact: true) flag would be better on a per-check directive basis?

[malerichc]

We could add a cachebust key to check directives, and if it is not there, assume its value is true. Something like:

-   directive: check
    url: https://www.usnews.com
    cachebust: false

Or:

-   directive: check
    url: https://www.usnews.com
    transformations:
        cachebust: false

The latter could also contain more options for toggling or changing the behavior of other URL-transformations on a per-directive basis.

[mcbridem]

Yes. I had a similar thought today, except it was:

-   directive: check
    url: https://www.usnews.com
    transformations: false

This would be the same as exact: true, just not in a redirect block?

If we went the list of transformations toggles route, what would we have besides cache_bust: false? level_mangling: false, as a complementary feature to only_levels? Any others?

[malerichc]

The only one I personally desire is toggling cachebusting. I definitely want to be able to turn off cachebusting but leave level-mangling on.