snort: add experimental PCRE2 support patch

snort: add experimental PCRE2 support patch

Add experimental PCRE2 support patch as PCRE is EOL and won't receive
any new updates anymore.

Since PCRE2 API changed, also snort plugins API changed and require some
tweka for any user downstream that compile custom plugins. The examples
are all updated and conversion patch contains additional info on the
changes required to the plugins.

Plugins needs to be compiled and require updates anyway so there isn't a
problem with user trying to load incompatible plugins.

Signed-off-by: Christian Marangi <[email protected]>