ruby: Document `use_bundler` configuration option (#22498) #10

Job	Run time
check_docs_only	15s
Check Postgres and Protobuf migrations, mergability	0s
Check formatting and spelling	0s
(Linux) Run Clippy and tests	0s
(macOS) Run Clippy and tests	0s
(Windows) Run Clippy and tests	0s
(Linux) Build Remote Server	0s
Create arm64 Linux bundle	0s
Create a Linux bundle	0s
Create a macOS bundle	0s
Auto release preview	0s
	15s

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