rec: reduce RPZ memory usage

[omoerbeek]

Short description

This PR contains two ways to reduce RPZ memory usage:

1. Use unique_ptrs for optional data in a Policy object. This reduces the memory used per RPZs by roughly 40% in typical cases.
2. Avoid keeping a reference to the Lua config object in the thread startup code. This avoid keeping the RPZs loaded at startup around after a rec_control reload-lua-config. Tested with rpzFile and rec_control reload-lua-config, but I suspect rpzPrimary has the same issue.

Fixes #13827 and fixes #12870 (duplicate)

Some memory usage data, first a clean startup wit a couple of RPZ loaded via rpzPrimary():

 1043 otto      10    0 2344M 2327M idle      fsleep    1:15  0.00% pdns_recursor <- master
68681 otto      10    0 1404M 1386M idle      fsleep    1:30  0.00% pdns_recursor <- PR code

On another test with a couple of RPZs loaded wit rpzFile:

      initial   1st  2nd 3rd reload
master    355   682  689 689
PR        218   226  232 232

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 8046905464

Details

• -46 of 153 (69.93%) changed or added relevant lines in 8 files are covered.
• 40 unchanged lines in 8 files lost coverage.
• Overall coverage decreased (-0.01%) to 59.188%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/recursordist/pdns_recursor.cc	0	2	0.0%
pdns/recursordist/rec-lua-conf.cc	0	5	0.0%
pdns/recursordist/filterpo.cc	39	47	82.98%
pdns/recursordist/filterpo.hh	36	45	80.0%
pdns/recursordist/lua-recursor4.cc	0	22	0.0%

Files with Coverage Reduction	New Missed Lines	%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
pdns/misc.hh	3	82.17%
pdns/recursordist/test-syncres_cc2.cc	3	88.85%
pdns/misc.cc	5	62.57%
pdns/signingpipe.cc	5	85.75%
pdns/dnsdist-carbon.cc	6	59.62%
pdns/dnsdist-tcp.cc	8	75.83%
pdns/packethandler.cc	8	72.82%

Totals
Change from base Build 8000517227:	-0.01%
Covered Lines:	113563
Relevant Lines:	158645

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💛 - Coveralls