fix: selection algo filtering on max price fixed

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What does this pull request do? Explain your changes. (required)

Fixes behavior of gateway when no max price is set. 0 maxPrice will return to being no max price filter enabled.

The addition of maxPricePerCapability included initializing a zero max price by default so the map is fully initialized. This broke the filterByMaxPrice function that checked for an unset maxPrice of nil.
Specific updates (required)

• updates filterByMaxPrice function in selection_algorithm.go to check for 0 rather than checking for nil
• added test to cover this so will fail in future if behavior of max price filtering changes
• updated TestFilter test to set a maxPrice of 0 if none set

How did you test each of these updates (required)

Added new test and ran all tests in selection_algorithm_test.go

Does this pull request close any open issues?

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass X selection_algorithm_test.go pass.
• README and other documentation updated
• Pending changelog updated

[victorges]

lgtm

[victorges]

thanks for adding tests 🙏

[ad-astra-video]

I updated for suggested change. Learned something new, did not know Sign() did that!