Add Default Options Value Override Feature

[MotorBottle]

已实现

实现默认参数的覆盖，可以修改一些参数的默认值而无需用户主动请求指定该参数的值。使用方法为在default主题的渠道设置中，以json格式指定需要覆盖参数的模型以及其对应的参数和值。

几个问题

1. 目前只针对默认主题添加了此功能，其他主题可以正常使用但如需使用新功能需要进一步适配
2. 目前支持默认覆盖的参数有限，如需针对一些模型的特定参数进行覆盖，可能需要用户手动添加。目前已支持的参数：temperature, max_tokens, top_p, frequency_penalty, presence_penalty, stop, n, stream, num_ctx。如需添加其它参数需前往relay/controller/text.go编辑applyParameterOverrides函数。
3. 没有接触过golang，代码可能存在不完善的部分，如有问题请feel free指出

close #1753

我已确认该 PR 已自测通过，相关截图如下：

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 100 lines in your changes missing coverage. Please review.

Project coverage is 1.20%. Comparing base (7e51b04) to head (b2cc54f).

Files with missing lines	Patch %	Lines
relay/controller/text.go	0.00%	83 Missing ⚠️
model/channel.go	0.00%	11 Missing ⚠️
relay/meta/relay_meta.go	0.00%	5 Missing ⚠️
middleware/distributor.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #1859      +/-   ##
========================================
- Coverage   1.21%   1.20%   -0.01%     
========================================
  Files        145     145              
  Lines      12235   12328      +93     
========================================
  Hits         149     149              
- Misses     12072   12165      +93     
  Partials      14      14              

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