Increase max path length

Problem/Motivation

With 4.x we now support D9+ minimal which has a requirement of MySQL 5.7.

MYSQL 5.7 enables innodb_large_prefix by default (and is not an option in newer versions) allowing a max key length of up to 3072b

This allows us to increase from 255 characters to 768 characters across all primary index fields while retaining support for UTF8-4-byte characters.

50 of these characters are currently consumed by the bucket machine name.

We may want to keep this below 718 characters to allow some additional room for future keys, such as 🐛 Issue with directories and trailing whitespaces Needs work

This becomes slightly more important as we now no longer store files based on scheme:// and instead use the full path into the bucket.

Steps to reproduce

Review s3fs_bucket_schema()

Proposed resolution

Increase length of path field.

Remaining tasks

Patch

User interface changes

None

API changes

Increase S3fsMetadataServiceInterface::MAX_PATH_LENGTH

Data model changes

Increase size of s3fs_file path field.