Apply metadata filters case insensitively

[imjoehaines]

Goal

In most of our notifiers, string filters are applied case insensitively as usually you'd always want to filter both 'password' and 'Password' — the casing doesn't matter

In the PHP library, filters have always been case sensitive, which caused issues when filtering cookies by default — the getallheaders PHP function (and our own fallback) use an uppercase first letter for header names (Cookie), but Laravel uses lowercase headers (cookie)

We could decide that headers should always be lowercased (or uppercased, or aLtErNaTe case) but this seems like a good excuse to bring PHP more inline with our other libraries

NB: PHP applies filters if a string contains the filter, rather than exactly matching. I think changing that would be considered a breaking change as it could result in us recording data that should have been filtered, whereas this change could only filter more data than before

Changeset

• Use stripos rather than strpos when checking if filters match
• Added more tests for filter matching