Add Android Request Interception

[jkmassel]

This initial implementation allows us to inject authentication at runtime if needed.

You can test it by making the demo app activity conform to GutenbergRequestInterceptor, then adding:

    override fun interceptRequest(request: WebResourceRequest): WebResourceRequest {

        if (request.url.host.isNullOrEmpty()) {
            return request
        }

        if (!request.url.host!!.contains("wordpress.com")) {
            return request
        }

        request.requestHeaders["Authorization"] =
            "Bearer [redacted – replace this string]"

        return request
    }

Once you've added a bearer token, copy the URL to an image on a private blog, and insert a new image block with that URL. The editor will now display it.

[dcalhoun]

I attempted testing this quickly by rebasing it atop #29 and using wordpress-mobile/WordPress-Android#21223 to build WordPress-Android with these changes.

When testing it this way—and without conforming to GutenbergRequestInterceptor—I experience CORS errors for all requests for the site's REST API. Below are screenshots of the network failures and one of the requests with and without these changes applied.

Screenshots

Request Failures	Request Example

I didn't spend time debugging it aside from inspecting the requests. Maybe some of the headers are erroneously discarded by the interception logic? WDYT?

Hopefully #29 and wordpress-mobile/WordPress-Android#21223 merge later today, which will simplify further testing. Update: The referenced pull requests are now merged.

[dcalhoun]

Friendly note: I rebased this atop the latest trunk branch to resolve merge conflicts to make testing easier.

[dcalhoun]

Changes look sound, testing plan succeeds for me. 🚀

Noting that I removed (69b8e54) the previously added okhttp dependencies from this change set, as the networking logic was hoisted to the host app.