Add option to enable tracing and move logfiles to project drectory

[kpodsiad]

Use case
Usually, I've multiple running instances of metals, and in order to see logs from a particular one I have to reload window, so this instance would be the last run one. It annoys me so much 😅

How it is
Currently, in order to enable JSON-RPC tracing user has to manually create files (see manual). In addition to that, those files are global and only the very last instance of metals can write to them.

How it could be
My proposition is to:

• move the logfiles from home to the current project directory, so logs will be project scoped
• (optionally) add an option to metals, something like "enable json-rpc tracing" switch, and get rid of creating empty files manually.

[tgodzik]

I think it's a good idea, though I would maybe add it as a new option? So if you create ~/.metals/lsp.trace.json it will only log there and not to the global one. What do you think?

[kpodsiad]

I couldn't agree with you more!