feat: HTTP method-aware web page caching

[kenjis]

Description
Closes #8363

Enhancement to https://codeigniter4.github.io/CodeIgniter4/general/caching.html

• add HTTP method to page cache key

The current issue:
If we use RESTful Resource Handling, operation Create and List have the same URI.
https://codeigniter4.github.io/CodeIgniter4/incoming/restful.html#presenter-controller-comparison
If we enable page caching to List (GET), Create (POST) will return the cached List response.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[lonnieezell]

So what's cachable? GET and HEAD? If that's all, and HEAD isn't something we really need to worry about caching, wouldn't it be simpler to just check if $request->getMethod() !== 'get'?

[michalsn]

ResponseCache also caches the headers, so in theory, it can be useful for HEAD... however, as I mentioned in my comment, I would make it configurable and stick to the GET by default.

[kenjis]

So what's cachable?

GET, HEAD, POST, PATCH, CLI.
But a dev must put $this->cachePage($n); in controller.

[michalsn]

But a dev must put $this->cachePage($n); in controller.

Ok, that changes a lot.

[kenjis]

I dropped the check.

To begin with, page caching must be specified by developers in controllers.
There is no need for the filter to dare to check the HTTP method to limit the cache functionality.

Besides, if a developer wants to determine to enable caching by HTTP method, they can customize the filter.

[michalsn]

Enabling caching for POST requests by default is rather controversial. I would be in favor of adding a config for this.

While I can imagine a scenario where we want to cache the POST response, the most common action for POST requests (which change the state of the application) will be to respond with new content every time.

[kenjis]

Ah, strictly speaking, the current this PR has a breaking change?
Because the current implementation (4.5) can cache any HTTP method request.

[michalsn]

LGTM

[kenjis]

I forgot to document. Added.

[lonnieezell]

LGTM