pyubx2 Pull Request Template

Description

Adding the sigId field from the UBX-RXM-SFRBX message, as described in recent u-blox documentation, e.g. u-blox F9 TIM 2.20 Interface Description (page 180)

No change in behavior

[x] I agree to abide by the code of conduct (see CODE_OF_CONDUCT.md).
[x] My code follows the style guidelines of this project (see CONTRIBUTING.MD).
[x] I have performed a self-review of my own code.
[x] (if appropriate) I have cited my u-blox documentation source(s).
[ ] I have commented my code, particularly in hard-to-understand areas.
[ ] I have made corresponding changes to the documentation.
[x] (if appropriate) I have added test cases to the tests/test_*.py unittest suite to maintain >= 99% code coverage.
[ ] I have tested my code against the full tests/test_*.py unittest suite.
[ ] My changes generate no new warnings.
[ ] Any dependent changes have been merged and published in downstream modules.
[x] I have signed my commits.
[x] I understand and acknowledge that the code will be published under a BSD 3-Clause license.