feat: add gzip pre-compression for static assets to improve load time

[RomanNikitenko]

What does this PR do?

• Pre-compresses JS/CSS/HTML/JSON files during Docker build (gzip -9)
• Serves .gz files directly when client supports Accept-Encoding: gzip
• Falls back to uncompressed files if .gz is missing or on any error
• Adds CODE_DISABLE_STATIC_GZIP=1 env variable as kill switch

Expected improvement:

• workbench.js transfer drops from ~16MB to ~4.4MB: (~3.7x reduction),
• significantly reducing white screen time https://redhat.atlassian.net/browse/CRW-10327
• zero risk of regression: if .gz files don't exist or env variable is set, the server behaves exactly as before

What issues does this PR fix?

https://redhat.atlassian.net/browse/CRW-10327

How to test this PR?

Does this PR contain changes that override default upstream Code-OSS behavior?

• the PR contains changes in the code folder (you can skip it if your changes are placed in a che extension )
• the corresponding items were added to the CHANGELOG.md file
• rules for automatic git rebase were added to the .rebase folder

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[rgrunber]

I'm not seeing a huge improvement in speed, but there's definitely less data being transferred. It might make a difference on slower connections.

Before

workbench.js	dom	load	finish (s)	total transfer
1.24s	334ms	4.39s	19.64s	19.82MB
770ms	436ms	3.94s	16.65s	19.82MB
508ms	447ms	3.85s	16.32s	19.82MB
1.05s	502ms	4.22s	17.09s	19.82MB
3.27s	437ms	6.36s	19.15s	19.82MB

After

workbench.js	dom	load	finish (s)	total transfer
894ms	447ms	4.24s	18.03s	6.40MB
793ms	287ms	4.03s	18.09s	6.40MB
635ms	437ms	3.89s	17.78s	6.36MB
567ms	362ms	3.78s	18.50s	6.36MB
472ms	232ms	3.64s	17.25s	6.36MB