feat: support fixed plugin path for development mode

[guqing]

What type of PR is this?

/kind feature /milestone 2.0 /area core

What this PR does / why we need it:

目前插件开发模式允许配置项目目录，但必须配置到项目目录的上一级，并不友好 此 PR 提供了 fixedPluginPath 选项允许在开发模式时配置它为插件项目目录 在开发 gradle 插件时更易于通过配置此选项来加载插件

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

/cc @halo-dev/sig-halo

Does this PR introduce a user-facing change?

None

[f2c-ci-robot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang, ruibaby

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