[ui] Add additional node information in the documentation tab

[Alxiice]

Description

This PR adds additional information on the Documentation tab of nodes.
Here are examples :

import os
from meshroom.core import desc

__version__ = "1.0"
__author__ = "moduleauthor"
__license__ = "MIT"

class TestCLNode(desc.CommandLineNode):
    category = 'TestPlugin'
    commandLine = 'command'
    
    documentation = """# TestCLNode
## Node info
here are info on the node

## How to use it
Here are more info
1. First step
2. Second step
"""

Also we can override parameters at the node level :

• "author" and "version" can be directly overrided
• It is possible to put any additional information in a __nodeInfo__ list

class TestCLNode2(desc.CommandLineNode):
    """# TestCLNode

## Node info
here are info on the node

## How to use it
Here are more info
1. First step
2. Second step
"""

    category = 'TestPlugin'
    author = "Alice"
    version = "2.0.0"
    __nodeInfo__ = [
        ("model link", "https://huggingface.co/alicevision/great-model")
    ]

Finally I also added the possibility to read the documentation from the class __doc__ parameterr

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.77%. Comparing base (de33f55) to head (2cb2c1a).
⚠️ Report is 7 commits behind head on develop.

Files with missing lines	Patch %	Lines
meshroom/core/node.py	76.92%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2802      +/-   ##
===========================================
+ Coverage    77.59%   77.77%   +0.18%     
===========================================
  Files           48       50       +2     
  Lines         6655     6728      +73     
===========================================
+ Hits          5164     5233      +69     
- Misses        1491     1495       +4     

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[fabiencastan]

I would suggest a simplication like this (with a fallback on the module):

class TestCLNode2(desc.CommandLineNode):
    """# TestCLNode

## Node info
here are info on the node

## How to use it
Here are more info
1. First step
2. Second step
"""

    category = 'TestPlugin'
    commandLine = 'python ' + exe_path
    author = "Alice"
    version = "2.0.0"

[cbentejac]

The documentation keys should be capitalized in the display but apart from that, everything is working well and ready to be merged!