Expose channel fees in ChannelDetails

[valentinewallace]

We need this to make route hints for invoices.

[TheBlueMatt]

Fee charged by us is usually not very useful/interesting, I suppose we could export it, but you almost certainly want the fee charged by our counterparty for inbound information, not the other way around - I believe thats the actual reason for #207.

[codecov]

Codecov Report

Merging #824 (7c7c08b) into main (4894d52) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #824      +/-   ##
==========================================
- Coverage   90.97%   90.95%   -0.02%     
==========================================
  Files          48       48              
  Lines       26452    26456       +4     
==========================================
- Hits        24064    24063       -1     
- Misses       2388     2393       +5     

Impacted Files	Coverage Δ
lightning/src/routing/router.rs	96.86% <ø> (ø)
lightning/src/ln/channelmanager.rs	85.22% <50.00%> (-0.07%)	⬇️
lightning/src/ln/functional_tests.rs	96.94% <0.00%> (-0.06%)	⬇️

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[valentinewallace]

Dangit, OK revising approach...