能否在配置文件中增加一个lcn控制开关

## Why you need it?
Is your feature request related to a problem? Please describe in details
我们有些项目，根据客户的场景需求，在部署的时候才能决定是否开启分布式事务（比如如果用不到lcn，就不用部署tm等）。因为是在部署阶段决定，所以通过修改代码@EnableDistributedTransaction的方式不太合适。
能否设置一个开关来控制lcn的启动与否，比如通过配置文件里面的某个参数来控制。

## How it could be?
A clear and concise description of what you want to happen. You can explain more about input of the feature, and output of it.
设置一个开关来控制lcn的启动与否，并且不用改代码的前提下，比如通过配置文件里面的某个参数来控制。

## Other related information
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Start by locating the handling for @EnableDistributedTransaction and the configuration-loading entry point. Trace how startup currently enables LCN, then define a configuration property that controls that behavior without code changes. Done means deployment configuration can enable or disable LCN consistently, with tests covering both settings.

Written by the indexing model from the issue text.