chore: Fix import of context package across codebase

[jannfis]

Several packages were importing context from golang.org/x/net/context, while it's been integrated into the standard library for some serious while now.

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[codecov]

Codecov Report

Merging #9852 (10d748a) into master (ee7356a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9852   +/-   ##
=======================================
  Coverage   45.86%   45.86%           
=======================================
  Files         227      227           
  Lines       26862    26862           
=======================================
  Hits        12320    12320           
  Misses      12862    12862           
  Partials     1680     1680           

Impacted Files	Coverage Δ
server/account/account.go	69.62% <ø> (ø)
server/application/application.go	31.46% <ø> (ø)
server/cluster/cluster.go	29.95% <ø> (ø)
server/repository/repository.go	52.41% <ø> (ø)
server/server.go	53.18% <ø> (ø)
util/db/certificate.go	75.66% <ø> (ø)
util/db/cluster.go	60.00% <ø> (ø)
util/db/repository.go	39.28% <ø> (ø)
util/db/repository_legacy.go	48.87% <ø> (ø)
util/db/repository_secrets.go	69.68% <ø> (ø)
... and 7 more

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[jannfis]

The linter complained about contextKey being of type string, so I wrapped it in its own type.

[crenshaw-dev]

lgtm!