fix: Run terminal command in the background

Description

When running command in the integrated terminal, TerminalManager will take into account silent flag passed in the RPC message payload from the LS and will run command silently (without opening terminal) if the flag is set to true.

Related Issues

Closes gitlab-org/editor-extensions/gitlab-lsp#1434 (closed)

How has this been tested?

1. Link current MR with LS change gitlab-org/editor-extensions/gitlab-lsp!2235 (merged)
2. Start extension in extension dev host
3. Make sure you have IDE terminal closed
4. Open Agentic chat and start the conversation. Initial message should include shell context but the IDE terminal should not open to run commands that detect shell environment or if it open you wan't see visible terminal processes for shell-detection and shell-env-detection

Screenshots (if appropriate)

You should not see this

But IDE terminal context will be included

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes