Allow the profilers to be plugged to multiple backends

What

Allow the profilers to be plugged to multiple backends

Why

Because this is what the documentation stated but it was not implemented like this

How

By storing a list of profilers instead of an option

Manually testing the MR

TEZOS_PPX_PROFILER=t make octez-layer1

Then

PROFILING="*->debug" PROFILING_BACKENDS="txt; json" ./octez-node run

You should see, in your data dir:

-rw-r--r-- 1 mattias mattias 176M Jun 17 16:44 block_validator_profiling.json
-rw-r--r-- 1 mattias mattias  24M Jun 17 16:44 block_validator_profiling.txt
-rw-r--r-- 1 mattias mattias 1.2M Jun 17 16:44 chain_validator_profiling.json
-rw-r--r-- 1 mattias mattias 530K Jun 17 16:44 chain_validator_profiling.txt
-rw-r--r-- 1 mattias mattias  304 Jun 17 16:41 config.json
drwxr-xr-x 1 mattias mattias  182 Jun 17 16:44 context
drwxr-xr-x 1 mattias mattias   36 Jun 17 16:41 daily_logs
-rw-r--r-- 1 mattias mattias  300 Jun 17 16:42 identity.json
-rw-r--r-- 1 mattias mattias    6 Jun 17 16:43 lock
-rw-r--r-- 1 mattias mattias 535K Jun 17 16:44 peer_validator_profiling.json
-rw-r--r-- 1 mattias mattias 229K Jun 17 16:44 peer_validator_profiling.txt
-rw-r--r-- 1 mattias mattias  16K Jun 17 16:42 peers.json
-rw-r--r-- 1 mattias mattias 528K Jun 17 16:44 rpc_server_profiling.json
-rw-r--r-- 1 mattias mattias 224K Jun 17 16:44 rpc_server_profiling.txt
drwxr-xr-x 1 mattias mattias   56 Jun 17 16:41 store
-rw-r--r-- 1 mattias mattias  12M Jun 17 16:44 store_profiling.json
-rw-r--r-- 1 mattias mattias 2.1M Jun 17 16:44 store_profiling.txt
-rw-r--r-- 1 mattias mattias   20 Jun 17 16:41 version.json

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR