Document the regex better in Memgraph

[Josipmrden]

we have 2 related flags --auth-user-or-role-name-regex= and --auth-password-strength-regex=
The regular expression syntax is based on the modified ECMAScript regular expression grammar. The ECMAScript grammar can be found here, while the modifications are described in this document. (if this is applied in all cases, just a quick verification needed), the same (or very similar sentence) should be located near

also, wherever regex is mentioned, we can either link to https://memgraph.com/docs/querying/clauses/where#3-regular-expressions

or some other dedicated place in Memgraph

[kgolubic]

We have three different regex-related situations:

1. For regex in WHERE clause, we use Modified ECMAScript regular expression grammar (https://en.cppreference.com/w/cpp/regex/ecmascript)
2. For text (https://memgraph.com/docs/advanced-algorithms/available-algorithms/text#regexgroups) we use C++ regex https://en.cppreference.com/w/cpp/regex
3. And for text search (https://memgraph.com/docs/configuration/text-search#regex-search), we use https://github.com/quickwit-oss/tantivy