Introduce backend-agnostic provider configuration and provider manager factory

[ChansAlive]

This PR refactors the crypto daemon's provider layer to be backend-agnostic and configurable at build and runtime.

Key changes:

• Added a new [backend] configuration layer that controls which cryptographic backends are compiled into the daemon via Bazel flags (backend_exports.bzl, backend_config.bzl).
• Introduced ProviderManagerFactory to register and create provider managers based on compile-time enabled backend families.
• Made ScoreProviderFactory backend-agnostic: it now discovers enabled score backends (e.g. OpenSSL, future Primula) through active_backends_list.hpp and selects the default backend via a configurable preference order.
• Made Pkcs11ProviderFactory support different PKCS#11 backends through a Bazel label_flag, replacing hardcoded SoftHSM dependencies.
• Removed hardcoded provider names (e.g. common::kProviderNameOpenSSL) in favor of names derived from backend adapters and config.
• Added backend adapter interfaces (score_backend_adapter, openssl_backend_adapter, pkcs11_token_config_parser) to decouple provider implementations from backend-specific details.
• Added documentation for the three-layer provider configuration model and a README for backend configuration.
• Added tests for backend config parsing and provider manager behavior.

Build impact:
Backends are now selected via [backend] flags. Existing OpenSSL and SoftHSM defaults are preserved.

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run --lockfile_mode=error //:license-check

Status: ⚠️ Needs Review

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[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.3.0) and connecting to it...
INFO: Invocation ID: e7632b94-cd0c-4dbf-b6cf-e3291296c13f
Computing main repo mapping: 
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DEBUG: Rule 'abseil-cpp+' indicated that a canonical reproducible form can be obtained by modifying arguments integrity = "sha256-m3oGQwXp/ZTRJP+mzDWFkutCtdpYj7TgfQklSqQAhts="
DEBUG: Repository abseil-cpp+ instantiated at:
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Repository rule http_archive defined at:
  /home/runner/.bazel/external/bazel_tools/tools/build_defs/repo/http.bzl:394:31: in <toplevel>
DEBUG: Rule 'protobuf+' indicated that a canonical reproducible form can be obtained by modifying arguments integrity = "sha256-w6Cp7OiTLjHDtzbi2xixxC5wcM2biBOIsm0BqnHiTKI="
DEBUG: Repository protobuf+ instantiated at:
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Repository rule http_archive defined at:
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Computing main repo mapping: 
DEBUG: Rule 'grpc+' indicated that a canonical reproducible form can be obtained by modifying arguments integrity = "sha256-CvN7gAlTEwtHwHW1ZoPuYL3D7aPDf8YAQZP1tWl1ggQ="
DEBUG: Repository grpc+ instantiated at:
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Repository rule http_archive defined at:
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Computing main repo mapping: 
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WARNING: Target pattern parsing failed.
ERROR: Skipping '//:license-check': no such target '//:license-check': target 'license-check' not declared in package '' defined by /home/runner/work/inc_security_crypto/inc_security_crypto/BUILD
ERROR: no such target '//:license-check': target 'license-check' not declared in package '' defined by /home/runner/work/inc_security_crypto/inc_security_crypto/BUILD
INFO: Elapsed time: 8.929s
INFO: 0 processes.
ERROR: Build did NOT complete successfully
ERROR: Build failed. Not running target

[github-actions]

The created documentation from the pull request is available at: docu-html