Change config load order so custom.toml is last

[Taztingo]

Description

This updates the configuration load order so that custom.toml is the last. This allows any custom changes to overwrite anything that comes packed or unpacked config.

closes: #1262

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #1684 (6ff0f77) into main (4279889) will increase coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1684      +/-   ##
==========================================
+ Coverage   64.77%   64.80%   +0.03%     
==========================================
  Files         261      261              
  Lines       31306    31308       +2     
==========================================
+ Hits        20279    20290      +11     
+ Misses       9746     9740       -6     
+ Partials     1281     1278       -3     

Files Changed	Coverage Δ
cmd/provenanced/config/manager.go	60.13% <100.00%> (+2.26%)	⬆️

[SpicyLemon]

Should have a changelog entry, then LGTM.

[nullpointer0x00]

Nice work!