Respect astGrep.configPath setting

[StevenLove]

We intend to support custom locations for sgconfig.yml, but some places still assume that it is only located in the workspace root and only named sgconfig.yml.

• add lspconfig check in check whether to start LSP client/server upon activating extension as per #227 #251
• add lsp config path in restart tests at src/test/restart.test.ts #250
• respect config in LSP in ast-grep project #249

Related #244