feat: apu fuel consumption

[tracernz]

Fixes #[issue_no]

Summary of Changes

This patch allows the APU to consume fuel (from the left inner tank).

Known issues not fixed by this PR:

• The APU has no fuel flow when the left inner tank fuel pumps are off (APU Fuel Flow 0 When Tank Pumps Off #8146).

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub):

Testing instructions

Check that the left inner tank fuel level reduces when the APU is running with the left inner tank pumps on.

How to download the PR for QA

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2. Click on the Checks tab on the PR
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[Taz5150]

Checked - APU consumes fuel from left tank at a rate of 33 gallons/ hour as expected.

[Saschl]

Tested as well. fuel consumption works as expected. (Already existing) Issue with fuel pumps necessary might be solved in another PR.

[donstim]

Just noticed that APU fuel consumption here is always drawn from the left inner tank. If the crossfeed valve is open, it should draw from both tanks.