lestarch: allowing GTest to be disabled in UTs

[LeStarch]

Originating Project/Creator	Infrastructure
Affected Component
Affected Architectures(s)
Related Issue(s)
Has Unit Tests (y/n)
Builds Without Errors (y/n)
Unit Tests Pass (y/n)
Documentation Included (y/n)

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Change Description

Allows users to disable GTest dependencies in UTs:

set(UT_INCLUDE_GTEST OFF)
fprime_register_ut(...

Rationale

GTest was always intended to be an optional addition to our unit tests. It helps the test, but should not be required. Thus we have the ability to turn it off.

Testing/Review Recommendations

None

Future Work

Ensure this feature is not lost in the move to v3.0.0