Add forwarding of scan requests

[ChrisspyB]

wip. todo:

• Make sure non-forwarded requests still work as expected.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 43.56061% with 149 lines in your changes missing coverage. Please review.

Project coverage is 61.62%. Comparing base (be8752e) to head (cb4a1ec).

Files with missing lines	Patch %	Lines
src/gribjump/Forwarder.cc	0.00%	54 Missing ⚠️
src/gribjump/remote/Request.cc	0.00%	24 Missing ⚠️
src/gribjump/remote/RemoteGribJump.cc	21.73%	18 Missing ⚠️
src/tools/gribjump-scan.cc	54.54%	15 Missing ⚠️
src/gribjump/Task.cc	27.77%	13 Missing ⚠️
src/gribjump/Engine.cc	67.64%	11 Missing ⚠️
src/gribjump/remote/Request.h	0.00%	6 Missing ⚠️
src/gribjump/URIHelper.h	72.72%	3 Missing ⚠️
src/gribjump/remote/GribJumpUser.cc	0.00%	2 Missing ⚠️
src/gribjump/Config.h	0.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #34      +/-   ##
===========================================
- Coverage    62.01%   61.62%   -0.39%     
===========================================
  Files           85       88       +3     
  Lines         4454     4576     +122     
  Branches       492      498       +6     
===========================================
+ Hits          2762     2820      +58     
- Misses        1692     1756      +64     

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