docs: freeze 6.3 CLI reference to static rST (OSMO-6482)

[samuelhanono-Nvidia]

Description

Freeze the 6.3 CLI reference pages to static reStructuredText so the
multiversion docs build renders this version's CLI without importing this
branch's code. Generated with make -C docs cli-rst in a 6.3 environment: each
page's argparse-with-postprocess directive is replaced by pre-rendered rST
(usage, options, sub-commands, examples) plus the cli_reference_* anchors that
other pages link to.

The deployed multiversion build introspects main's live CLI parser for every
version. 6.3 ships osmo bucket and osmo dataset (both removed on main), so
its live CLI directives raised NavigationException against main's parser and
broke the docs deploy. Freezing renders these pages from 6.3's own parser —
accurate to what 6.3 shipped and import-free.

Also widen the osmo credential --payload help table's third column so the
DATA row (region, override_url, addressing_style) renders as a valid grid
table. This fixes a pre-existing malformed-table error that only surfaced once
6.3's pages began building. The fix is applied in src/cli/credential.py so the
terminal --help output is correct too, then reflected in the regenerated page.

Adds the cli-rst make target and generate_cli_rst.py so the frozen pages can
be regenerated, mirroring the 6.1 (#1146) and 6.2 (#1147) freezes.

Validated with a local multiversion build (smv_prefer_remote_refs=False
against this branch): all versions build with zero warnings, 6.3's pages render
with no placeholders, and all cross-references resolve.

Issue #None

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/freeze-cli-rst-6.3

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