fix(entrypoint): improve PHP error detection for version checks

[joshtrichards]

We pull poll the image version sand installed version strings by calling php from the command line.

When this fails -- such as when a PHP module has problems loading (e.g. see #2509) we the version strings aren't populated correctly and the output is very confusing because the error output mangles things:

Can't start Nextcloud because the version of the data (
Warning: Cannot load module "memcached" because required module "igbinary" is not loaded in Unknown on line 0
Warning: Cannot load module "redis" because required module "igbinary" is not loaded in Unknown on line 0
32.0.2.2) is higher than the docker image version (
Warning: Cannot load module "memcached" because required module "igbinary" is not loaded in Unknown on line 0
Warning: Cannot load module "redis" because required module "igbinary" is not loaded in Unknown on line 0
32.0.3.2) and downgrading is not supported. Are you sure you have pulled the newest image version?

This makes the version string loading much more robust. Specifically it adds:

• Exit code checking
• Error message detection in output
• Version format validation

Catches:

• PHP crashes/fatal errors (exit code)
• PHP warnings/errors that don't cause non-zero exit (grep)
• Unexpected output format (version regex)