Switch the "Dot Path" option to optional

[lisez]

Environments:

• OS: Windows 11
• Obisidan v1.6.3
• plugin version 1.8.0

When I used some syntax, it shows:

and it is ok in my computer:

PS C:\Users\lisez> java -jar C:\Users\lisez\.bin\plantuml.jar -testdot
Dot version: dot - graphviz version 2.44.1 (20200629.0846)
Installation seems OK. File generation OK

I found it is a required argument to generate digams:

obsidian-plantuml/src/processors/localProcessors.ts

Line 194 in 2463d93

this.plugin.settings.javaPath, '-jar', '"' + jarFullPath + '"', '-Djava.awt.headless=true', '-charset', 'utf-8', '-graphvizdot', '"' + this.plugin.settings.dotPath + '"'

Then accroding to the PlantUML official site, it says "Starting from 1.2020.21... you don't need to manually install GraphViz anymore" on Windows.

Hence I think it maybe a goodtime to switch this option to optional.