chore: Add 'and' to this string

Description

Updates src/common/chat/gitlab_chat_slash_commands.ts to add a needed word to this string:

Reset conversation, and ignore the previous messages.

Related Issues

• Related to [JetBrains] Add /clear Command to Chat (gitlab-org/editor-extensions/gitlab-jetbrains-plugin#306 - closed)
• Related to chore: Add 'and' to smooth out clause (gitlab-org/editor-extensions/gitlab-jetbrains-plugin!409 - merged) (JetBrains fix)

How has this been tested?

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap