fix(mods): metamod gamemode fix

[pcace]

Description

Only applies if metamod addon is installed on a cs2 server:
currently the gamemode.gi gets overwritten when updating the cs2 installation, but metamod needs to be referenced in the gamemod.gi by:
Game csgo/addons/metamod

this fix adds the needed integration of metamod to the gamemod.gi file if it is not there and if metamod is installed.

Fixes #4492

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).

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 checked that this code is commented where required.
• I have provided a detailed enough description of this PR.
• I have checked if documentation needs updating.

Documentation

If documentation does need updating either update it by creating a PR (preferred) or request a documentation update.

• User docs: https://github.com/GameServerManagers/LinuxGSM-Docs
• Dev docs: https://github.com/GameServerManagers/LinuxGSM-Dev-Docs

Thank you for your Pull Request!

[dgibbs64]

I feel like this is an issue that should be dealt with by metamod rather LinuxGSM creating this type of fix. Are there any metamod discussions about this issue and any long term fixes?