IF: signature-provider for BLS keys

[heifner]

Currently signature-provider for BLS keys are specified as:

--signature-provider PUB_BLS_PAD80INyOVD3K0KJdl/7b5+UQGT0nrr8MDxO0tB80HMmaQS+X8YWRrYyyb7slAYFbOV69KN/skAFJfIFgdEEvD00MNhyaSJaJ1NGJjdKfq+OARJKoMBoBvj5/78n6BgLDpoJ7A===KEY:PVT_BLS_cvOsv1fAUDVgcK/J1j3U1DfQWMrmSFZDMiu4E0yJCEDWWZl3

The separator between the public key and private key is =KEY:. This can cause confusion since the base64 encoded public key also often ends in =. This follows the current separator between EOS keys:

--signature-provider EOS5VLjLL9nY5b2QymL8QVpwRnUDEhaedeHvVJ4vU8tpaEbxAwDc3=KEY:5JpgeNa7fAf4mXukVHmnNPqcN7qHbrp4NkMJQp32c1MbrLLdwYz

Consider a different separator for BLS keys provided to signature-provider.

Also the current implementation finds the first = and uses it to separate out the public key from the private key. This is clearly wrong for base64 encoded keys.
https://github.com/AntelopeIO/leap/blob/hotstuff_integration/plugins/signature_provider_plugin/signature_provider_plugin.cpp#L43

If the existing separator of =KEY: is maintained the parsing needs to be fixed.

Currently malformed signature-provider specifications do not stop nodeos. It ignores the error and continues. Seems this should stop nodeos from starting.

error 2024-01-09T22:46:19.780 nodeos    producer_plugin.cpp:1143      plugin_initialize    ] Malformed signature provider: "PUB_BLS_PAD80INyOVD3K0KJdl/7b5+UQGT0nrr8MDxO0tB80HMmaQS+X8YWRrYyyb7slAYFbOV69KN/skAFJfIFgdEEvD00MNhyaSJaJ1NGJjdKfq+OARJKoMBoBvj5/78n6BgLDpoJ7A===KEY:PVT_BLS_cvOsv1fAUDVgcK/J1j3U1DfQWMrmSFZDMiu4E0yJCEDWWZl3": {"code":10,"name":"assert_exception","message":"Assert Exception","stack":[{"context":{"level":"error","file":"common.hpp","line":61,"method":"apply","hostname":"","thread_name":"nodeos","timestamp":"2024-01-09T22:46:19.780"},"format":"false: No matching suite type for ${prefix}_${data}","data":{"prefix":"BLS","data":"PAD80INyOVD3K0KJdl/7b5+UQGT0nrr8MDxO0tB80HMmaQS+X8YWRrYyyb7slAYFbOV69KN/skAFJfIFgdEEvD00MNhyaSJaJ1NGJjdKfq+OARJKoMBoBvj5/78n6BgLDpoJ7A"}}]}, ignoring!