feat(cs2server): add Metamod:Source 2.0 and CounterStrikeSharp mod support

[borzaka]

Description

Add Metamod:Source 2.0 and CounterStrikeSharp support for Counter-Strike 2 through the existing mods-install, mods-update, and mods-remove commands.

• Add metamodsource2 for CS2 using the latest Metamod:Source 2.0 development build.
• Manage the required gameinfo.gi search path without adding duplicate entries. Restore missing entries during mod updates and remove them during uninstallation.
• Stop installation or updates if the required gameinfo.gi entry cannot be configured.
• Add counterstrikesharp using the latest GitHub release's Linux with-runtime archive for both installation and updates.
• Require LinuxGSM-managed metamodsource2 before installing CounterStrikeSharp.
• Preserve the shared Metamod directory when removing CounterStrikeSharp, while removing its own VDF.

Both mods install into game/csgo and are available only for CS2. Existing Source-engine Metamod support remains unchanged.

Fixes #4683 (partly; not all requested plugins are included here, just the 2 basic)
Fixes #4416
Fixes #4492
Closes #4500 (invalidates)

Type of change

• Bug fix (a change which fixes an issue).
• New feature (a change which adds functionality).
• New Server (new server added).
• Refactor (restructures existing code).
• Comment update (typo, spelling, explanation, examples, etc).

Testing

• Commands/tests run:
  • ./cs2server mods-install
  • ./cs2server mods-update
  • ./cs2server mods-remove
• Result: Metamod:Source 2.0 installed, CounterStrikeSharp installed, Mods update complete, CounterStrikeSharp removed, Metamod:Source 2.0 removed
• Environment used (distro/version): Ubuntu 22.04.5 LTS.

Risk and rollback

• Risk level: medium - Metamod installation modifies the CS2 gameinfo.gi file.
• Rollback plan: Remove CounterStrikeSharp first, then Metamod:Source 2.0 through mods-remove. Metamod removal deletes its search-path entry without replacing the rest of gameinfo.gi.

Breaking changes

• No breaking changes.
• Breaking changes included (describe below).

Documentation impact

• No documentation update required.
• User documentation update required.
• Developer documentation update required.

Checklist

PR will not be merged until all steps are complete.

• This pull request links to an issue.
• This pull request uses the develop branch as its base.
• This pull request subject follows the Conventional Commits standard.
• This code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have provided a detailed enough description of this PR.

Documentation

A user documentation update is requested for the new CS2 mod support. No documentation changes are included in this PR.