Page cache should strip unnecessary data from the response

Can't remove cacheability metadata - it might require creating a new response object from the old response or something to do that, but attachments can be removed it looks like.

We can create a minimal response object with only the information we need.

This doesn't make anything measurably faster according to a quick test with ab, but it does make it measurably smaller - so potentially still worth doing.

Before:

Server Software:        Apache/2.4.56
Server Hostname:        drupal-dev.ddev.site
Server Port:            443
SSL/TLS Protocol:       TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Server Temp Key:        X25519 253 bits
TLS Server Name:        drupal-dev.ddev.site

Document Path:          /node/1
Document Length:        43720 bytes

Concurrency Level:      1
Time taken for tests:   4.660 seconds
Complete requests:      500
Failed requests:        0
Total transferred:      22073000 bytes
HTML transferred:       21860000 bytes
Requests per second:    107.31 [#/sec] (mean)
Time per request:       9.319 [ms] (mean)
Time per request:       9.319 [ms] (mean, across all concurrent requests)
Transfer rate:          4626.08 [Kbytes/sec] received

MariaDB [db]> SELECT LENGTH(data) FROM cache_page;
+--------------+
| LENGTH(data) |
+--------------+
|        52133 |
+--------------+

After:

Server Software:        Apache/2.4.56
Server Hostname:        drupal-dev.ddev.site
Server Port:            443
SSL/TLS Protocol:       TLSv1.2,ECDHE-RSA-AES128-GCM-SHA256,2048,128
Server Temp Key:        X25519 253 bits
TLS Server Name:        drupal-dev.ddev.site

Document Path:          /node/1
Document Length:        43720 bytes

Concurrency Level:      1
Time taken for tests:   4.682 seconds
Complete requests:      500
Failed requests:        0
Total transferred:      22073000 bytes
HTML transferred:       21860000 bytes
Requests per second:    106.79 [#/sec] (mean)
Time per request:       9.364 [ms] (mean)
Time per request:       9.364 [ms] (mean, across all concurrent requests)
Transfer rate:          4604.00 [Kbytes/sec] received

MariaDB [db]> SELECT LENGTH(data) FROM cache_page;
+--------------+
| LENGTH(data) |
+--------------+
|        45250 |
+--------------+

Seems to have a test failure.

Remove library, drupal settings and other attachments from response.