debug: properly handle interrupted profiles

[prattmic]

By default (i.e., without profile.NoShutdownHook), profile.Start listens
for SIGINT and will stop the profile and call os.Exit(0).

restic already listens for SIGINT and runs its own cleanup handlers
before calling os.Exit(0).

As is, these handlers are racing when an interrupt occurs, and in my
experience, restic tends to win the race, resulting in an unusable
profile.

Eliminate the race and properly stop profiles on interrupt by disabling
package profile's signal handler and instead stop the profile in a
restic cleanup handler.

[codecov-io]

Codecov Report

Merging #1191 into master will decrease coverage by 5.76%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1191      +/-   ##
==========================================
- Coverage   52.93%   47.17%   -5.77%     
==========================================
  Files         126      126              
  Lines       12059    12055       -4     
==========================================
- Hits         6384     5687     -697     
- Misses       4930     5678     +748     
+ Partials      745      690      -55

Impacted Files	Coverage Δ
cmd/restic/main.go	8% <ø> (+0.45%)	⬆️
cmd/restic/global_release.go	0% <ø> (ø)	⬆️
internal/backend/b2/b2.go	0% <0%> (-79.32%)	⬇️
internal/backend/swift/swift.go	0% <0%> (-73.9%)	⬇️
internal/backend/azure/azure.go	0% <0%> (-61.93%)	⬇️
internal/backend/gs/gs.go	0% <0%> (-59.85%)	⬇️
internal/backend/swift/config.go	34.37% <0%> (-56.25%)	⬇️
internal/archiver/archiver.go	64.79% <0%> (-0.17%)	⬇️

---

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[fd0]

Cool, this is indeed much nicer. Thank you very much for your contribution!