ci: Doc: Move all config comments right next to the option they explain #36052

This is a CI doc-style-cleanup. BITCOIN_CONFIG is a single manually-formatted large string. This is fine, but shellcheck doesn't like when trailing comments are added: SC2155 -- Declare and assign separately.

Fix this style by using printf to format the single string. The second commit then moves the comments right into (or next to) the line that it concerns.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36052.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #36033 ([wip,nomerge,rfc] build: Require C++23 compiler by maflcko)
• #35957 (ci: Enable Boost.MultiIndex invariant-checking mode by hebasto)
• #35468 (ci, iwyu: Request IPC file generation explicitly by hebasto)
• #29700 (kernel, refactor: return error status on all fatal errors by ryanofsky)
• #26022 (Add util::ResultPtr class by ryanofsky)
• #25722 (refactor: Use util::Result class for wallet loading by ryanofsky)
• #25665 (refactor: Add util::Result failure types and ability to merge result values by ryanofsky)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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ACK fa03706fdef52e85b36b758c5867519acfc32a70.