Add support for environment variables

[danielfernau]

Adds support for environment variables to be used instead of command line options/arguments

For the download command:

• PROTECT_ADDRESS for --address
• PROTECT_PORT for --port
• PROTECT_NOT_UNIFI_OS for --not-unifi-os
• PROTECT_USERNAME for --username
• PROTECT_PASSWORD for --password
• PROTECT_VERIFY_SSL for --verify-ssl
• PROTECT_CAMERAS for --cameras
• PROTECT_WAIT_BETWEEN_DOWNLOADS for --wait-between-downloads
• PROTECT_IGNORE_FAILED_DOWNLOADS for --ignore-failed-downloads
• PROTECT_SKIP_EXISTING for --skip-existing-files
• PROTECT_TOUCH_FILES for --touch-files
• PROTECT_USE_SUBFOLDERS for --use-subfolders (use true or 1)/--no-use-subfolders (use false, 0, or omit env var)
• PROTECT_DOWNLOAD_TIMEOUT for --download-request-timeout
• PROTECT_START_TIME for --start
• PROTECT_END_TIME for --end
• PROTECT_DISABLE_ALIGNMENT for --disable-alignment
• PROTECT_DISABLE_SPLITTING for --disable-splitting
• PROTECT_CREATE_SNAPSHOT for --snapshot
• PROTECT_USE_UTC for --use-utc-filenames

For the events command

• PROTECT_ADDRESS for --address
• PROTECT_PORT for --port
• PROTECT_NOT_UNIFI_OS for --not-unifi-os
• PROTECT_USERNAME for --username
• PROTECT_PASSWORD for --password
• PROTECT_VERIFY_SSL for --verify-ssl
• PROTECT_CAMERAS for --cameras
• PROTECT_WAIT_BETWEEN_DOWNLOADS for --wait-between-downloads
• PROTECT_IGNORE_FAILED_DOWNLOADS for --ignore-failed-downloads
• PROTECT_SKIP_EXISTING for --skip-existing-files
• PROTECT_TOUCH_FILES for --touch-files
• PROTECT_USE_SUBFOLDERS for --use-subfolders (use true or 1)/--no-use-subfolders (use false, 0, or omit env var)
• PROTECT_DOWNLOAD_TIMEOUT for --download-request-timeout
• PROTECT_START_TIME for --start
• PROTECT_END_TIME for --end
• PROTECT_DOWNLOAD_MOTION_HEATMAPS for --download-motion-heatmaps
• PROTECT_USE_UTC for --use-utc-filenames

For the sync command

• PROTECT_ADDRESS for --address
• PROTECT_PORT for --port
• PROTECT_NOT_UNIFI_OS for --not-unifi-os
• PROTECT_USERNAME for --username
• PROTECT_PASSWORD for --password
• PROTECT_VERIFY_SSL for --verify-ssl
• PROTECT_CAMERAS for --cameras
• PROTECT_IGNORE_FAILED_DOWNLOADS for --ignore-failed-downloads
• PROTECT_USE_UTC for --use-utc-filenames
• PROTECT_SYNC_STATEFILE for --statefile
• PROTECT_SYNC_IGNORE_STATE for --ignore-state

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Implements and closes #385