prompt for asking user for WRKUSRJOB and WRKSPLF

[buzzia2001]

Changes

WRKSPLF and WRKUSRJOB now work on a single user profile instead of the whole system.
Both commands ask for a user profile when opened, pre-filled with *CURRENT (the connected profile). They still accept the user as an argument, in which case no prompt is shown. The selected user is shown in the tab title and above the table.

How to test this PR

1. Connect to an IBM i system, click FS Quick Start and select WRKSPLF: the prompt appears pre-filled with *CURRENT. Press Enter and check that only your spooled files are listed and that the title reads Work with Spooled Files - *CURRENT.
2. Open it again and enter another user profile: the table and the title follow that user. Enter an invalid name (1BAD NAME): validation fails. Press Esc: no view is opened.
3. Search, change page, refresh and delete a spooled file: the user filter must be kept every time.
4. Repeat with WRKUSRJOB, checking that Details, Hold, Release and End still work and keep the filter.
5. Run both commands from the command palette to confirm the prompt appears there too.

Checklist

• have tested my change
• have created one or more test cases
• updated relevant documentation
• Remove any/all console.logs I added
• have added myself to the contributors' list in CONTRIBUTING.md

Close #59

[buzzia2001]

vscode-ibmi-fs-1.0.8-dev.0.vsix.zip