expose regex query

[alex-au-922]

Exposed the regex query function based on the rust version's crate documentation.

Expected usage:

@staticmethod
def regex_query(schema: Schema, field_name: str, regex_pattern: str) -> Query:
    ...

query = Query.regex_query(index.schema, "body", "fish")

Raises error if the field name doesn't found, or the regex pattern is not valid.

Currently this query must be created outside from the query parser

[cjrh]

@alex-au-922 If you can fix up the conflicts (from merging your other BooleanQuery PR) I'll merge this one as well.

[alex-au-922]

Thanks, will fix it soon

[cjrh]

All good, I'm not rushing you 😄 . Whenever you have time.

[cjrh]

Oops sorry for the conflicts again. Should I have merged this one before boost query?

Anyway, we're getting there. After the conflicts are fixed here we can merge this too.

[alex-au-922]

I have updated the conflicts with boost query now. Thanks!