feat: accept snake_case environment variable names

[Brian Gordon Davis (bgdnext64)]

Adds support for snake_case environment variable names in addition to the existing concatenated form, addressing the readability concern raised in the issue.

Previously each flag mapped to a single environment variable built by uppercasing the flag name (for example subscriptionID → MPF_SUBSCRIPTIONID). MPF now also binds a snake_case variant derived from the flag's word boundaries, so MPF_SUBSCRIPTION_ID and MPF_SP_CLIENT_SECRET work too.

Details:

• Added camelCaseToSnakeUpper, which splits a camelCase flag name on word/acronym boundaries (e.g. subscriptionID → SUBSCRIPTION_ID, spClientID → SP_CLIENT_ID).
• bindFlags now explicitly binds each viper key to both the legacy concatenated env var and the snake_case env var, so existing setups keep working with no change. When both are set, the concatenated form takes precedence.
• Documented the alias behavior in the command-line flags reference.

Tests:

• TestCamelCaseToSnakeUpper covers the conversion across all global flags.
• TestBindEnvVars verifies both the legacy and snake_case forms resolve correctly, with per-subtest isolation from any pre-existing MPF_* variables.

Fixes #248

[Mani Bindra (maniSbindra)]

Hi Brian Gordon Davis (@bgdnext64) PR #298 addresses the same issue. Closing this issue