samples: introduce GOLIOTH_SAMPLE_TEST_CONNECT_TIMEOUT

[mniestroj]

Introduce connect timeout as a build configuration, so that test scripts will know how much time to wait before considering connection timeout. Having it as Kconfig option allows to configure it per platform and per connectivity requirements.

This replaces custom --initial-timeout pytest argument, which resulted in duplicating test cases for fast (default 30s) / long (configured 120s) timeouts.

[github-actions[bot]]

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