fix: configurable temp file directory #1028

Job	Run time
tests / Run (ubuntu-latest)	36s
examples / client (ubuntu-latest)	11s
examples / client (macos-latest)	16s
tests / Run (macos-latest)	1m 30s
examples / client (windows-latest)	1m 20s
tests / Run (windows-latest)	2m 23s
examples / multirepo (ubuntu-latest)	6s
examples / repository (ubuntu-latest)	4s
examples / multirepo (macos-latest)	17s
examples / root-signing (ubuntu-latest)	14s
examples / repository (macos-latest)	12s
examples / multirepo (windows-latest)	2m 1s
examples / root-signing (macos-latest)	24s
examples / repository (windows-latest)	1m 15s
examples / root-signing (windows-latest)	2m 5s
examples / tuf-client-cli (ubuntu-latest)	10s
linting / golangci-lint	16s
examples / tuf-client-cli (macos-latest)	21s
linting / govulncheck	13s
examples / tuf-client-cli (windows-latest)	1m 53s
	15m 47s

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