Support multiple GobPie confs in single workspace

[sim642]

Currently, GobPie assumes that gobpie.json is located at the root of the workspace where the IDE has been opened.

This could be relaxed to allow gobpie.json file to be located also in some subdirectory of the open workspace, GobPie just search the workspace for these files. Any paths and commands in gobpie.json should then be executed relative to it.

This could also allow multiple gobpie.json files to coexist in different subdirectories. Each one could correspond to an independent Goblint server, but the messages would be shown together in the single IDE instance.

[sim642]

Actually, GobPie shouldn't eagerly start a server for each gobpie.json it finds on startup because it could have very undesired effects if there are many (e.g. our bench repo). A more reasonable alternative is the following:

1. If gobpie.json exists in project root, use it automatically.
2. For other gobpie.jsons don't use them automatically, but only after the user has opened the conf file once.