config: Add `MBED_GREENTEA_TEST_RESET_TIMEOUT`

[LDong-Arm]

Description

Targets that take longer to boot (e.g. TF-M targets which boot MCUboot and TF-M before application) have forced_reset_timeout in mbed-os/targets/targets.json to increase timeout after reset before starting a Greentea test. This is previously handled by mbedgt, but as we move to CTest and mbedhtrun, a target's reset timeout needs to be available in CMake and passed to mbedhtrun.

Test Coverage

• [x] This change is covered by existing or additional automated tests.
• [ ] Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• [ ] Additional tests are not required for this change (e.g. documentation update).

[codecov[bot]]

Codecov Report

Merging #301 (98bc93c) into master (82a5802) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #301   +/-   ##
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  Coverage   97.08%   97.08%           
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  Files          92       92           
  Lines        2782     2782           
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  Hits         2701     2701           
  Misses         81       81           

[LDong-Arm]

We should probably have a test for this in tests/build/test_generate_config.py.

Done, tests added.