Audit issue 6: Use primary governance channel

[vgeddes]

Send force_update_channel and force_transfer_native_from_agent commands via primary governance channel.

In parachain/pallets/system/src/lib.rs:489-490, forceful channel updates, which include actions such as pausing or resuming a channel and adjusting usage fees, are currently directed through the secondary governance channel.

However, updates for the primary governance channel are being dispatched through the same channel as updates for all other channels.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (738ae56) 81.27% compared to head (55df029) 81.27%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1050   +/-   ##
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  Coverage   81.27%   81.27%           
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  Files          54       54           
  Lines        2238     2238           
  Branches       71       71           
=======================================
  Hits         1819     1819           
  Misses        402      402           
  Partials       17       17           

Flag	Coverage Δ
rust	81.43% <100.00%> (ø)

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[yrong]

LGTM!