Make GenerateMetadata robust to sessions without trials

[alexpiet]

Pull Request instructions:

• Please follow the update protocol
• Answer the questions below in detail. Your responses will be emailed to experimenters.
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• If computer maintainers need to manually update anything, provide detailed step by step instructions
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Describe changes:

• GenerateMetadata generates an error during habituation sessions. This is because the attribute self.behavior_software isn't created unless trials were generated. This doesn't make sense since the software is being used regardless. I moved the function that creates this attribute outside of the behavior_stream function.

What issues or discussions does this update address?

• resolves https://github.com/AllenNeuralDynamics/dynamic_foraging_error_tracking/issues/9

Describe the expected change in behavior from the perspective of the experimenter

• none

Describe any manual update steps for task computers

• none

Was this update tested in 446/447?

• tested

Does this update impact downstream processing by adding new saved files, or changing their format? If so, have you documented changes?

• No. The upload manifest won't be generated unless a trial is performed, so habituation sessions will not be uploaded.

[alexpiet]

@XX-Yin @hanhou @micahwoodard This is ready for review

[XX-Yin]

This is an update I have made in #1267 and #1265, which has not been merged.

It's good to merge this one.