Enhance --profile to load external profiles

[usmansaleem]

PR description

Add support to load external profiles using --profile option. The external profiles are expected to be placed in profiles directory under besu home (similar to plugins directory). This can be overridden using system property besu.profiles.dir. Running ./besu --help should report internal profiles along with external profiles - file names without .toml extension.

External profiles can be used to create custom Besu bundles with various plugins and their default options.

Example setup:

• Create profiles directory under besu home
• Create profiles/custom_profile.toml with configuration values to override.
• Use ./besu --profile=custom_profile ... to load the custom profile

Docs link: https://besu.hyperledger.org/public-networks/how-to/use-configuration-file/profile

Fixed Issue(s)

#7265

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• [x] unit tests: ./gradlew build
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• [x] integration tests: ./gradlew integrationTest
• [x] reference tests: ./gradlew ethereum:referenceTests:referenceTests