Feature: 添加插件元信息定义

[yanyongyu]

related issue: #1015

example plugin:

from pydantic import BaseModel

from nonebot.plugin import PluginMetadata


class Config(BaseModel):
    custom: str = ""


__plugin_meta__ = PluginMetadata(
    name="测试插件",
    description="测试插件元信息",
    usage="无法使用",
    config=Config,
    extra={"author": "NoneBot"},
)

[codecov]

Codecov Report

Merging #1046 (7f3a6bc) into master (ae21bfd) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1046      +/-   ##
==========================================
+ Coverage   77.96%   78.06%   +0.10%     
==========================================
  Files          42       42              
  Lines        3163     3178      +15     
==========================================
+ Hits         2466     2481      +15     
  Misses        697      697              

Flag	Coverage Δ
unittests	78.06% <100.00%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nonebot/plugin/__init__.py	96.72% <100.00%> (+0.05%)	⬆️
nonebot/plugin/manager.py	93.65% <100.00%> (+0.10%)	⬆️
nonebot/plugin/plugin.py	100.00% <100.00%> (ø)
nonebot/log.py	100.00% <0.00%> (ø)
nonebot/config.py	100.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ae21bfd...7f3a6bc. Read the comment docs.

[github-actions]

🚀 Deployed on https://deploy-preview-1046--nonebot2.netlify.app

[mnixry]

那个插件加载钩子函数有考虑加一下吗👀

[yanyongyu]

那个插件加载钩子函数有考虑加一下吗eyes

我觉得这个没有必要了，因为你要让插件加载的时候触发hook你首先得有hook，而hook又需要从插件里加载，这个会导致插件加载顺序出问题