Define domain specific workers in `php_server` and `php` blocks #2542

Job	Run time
prepare	20s
build (php-8-2-28-alpine, linux/amd64)	4m 45s
build (php-8-2-28-alpine, linux/386)	4m 42s
build (php-8-2-28-alpine, linux/arm/v7)	4m 48s
build (php-8-2-28-alpine, linux/arm64)	4m 59s
build (php-8-2-28-bookworm, linux/amd64)	1m 37s
build (php-8-2-28-bookworm, linux/386)	2m 24s
build (php-8-2-28-bookworm, linux/arm/v7)	2m 12s
build (php-8-2-28-bookworm, linux/arm64)	1m 55s
build (php-8-3-20-alpine, linux/amd64)	5m 1s
build (php-8-3-20-alpine, linux/386)	3m 52s
build (php-8-3-20-alpine, linux/arm/v7)	4m 15s
build (php-8-3-20-alpine, linux/arm64)	4m 53s
build (php-8-3-20-bookworm, linux/amd64)	1m 37s
build (php-8-3-20-bookworm, linux/386)	1m 53s
build (php-8-3-20-bookworm, linux/arm/v7)	2m 36s
build (php-8-3-20-bookworm, linux/arm64)	2m 4s
build (php-8-4-6-alpine, linux/amd64)	4m 41s
build (php-8-4-6-alpine, linux/386)	4m 57s
build (php-8-4-6-alpine, linux/arm/v7)	4m 16s
build (php-8-4-6-alpine, linux/arm64)	5m 43s
build (php-8-4-6-bookworm, linux/amd64)	1m 52s
build (php-8-4-6-bookworm, linux/386)	1m 57s
build (php-8-4-6-bookworm, linux/arm/v7)	2m 34s
build (php-8-4-6-bookworm, linux/arm64)	1m 45s
push	0s
	1h 21m 38s

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