Add Arduino_LowPowerPortentaH7 library

[sebromero]

This PR adds the Arduino_LowPowerPortentaH7 library to the index.

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/arduino-libraries/Arduino_LowPowerPortentaH7:

Linting library in Arduino_LowPowerPortentaH7
WARNING: library.properties name value Arduino_LowPowerPortentaH7 is longer than the recommended length of 16           
         characters.                                                                                                    
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format         
         (Rule LP010)                                                                                                   

Linter results for project: 0 ERRORS, 1 WARNINGS

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Linting sketch in Arduino_LowPowerPortentaH7/examples/AllowDeepSleep

Linter results for project: no errors or warnings

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Linting sketch in Arduino_LowPowerPortentaH7/examples/DeepSleepLockDebug

Linter results for project: no errors or warnings

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Linting sketch in Arduino_LowPowerPortentaH7/examples/Standby

Linter results for project: no errors or warnings

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Linter results for projects: 0 ERRORS, 1 WARNINGS

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/arduino-libraries/Arduino_LowPowerPortentaH7/