Doc exec build improved

[parmentelat]

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slight changes in page 'Executable Content → Execute during build'

mostly try to improve the right-hand-side toc for this page

• shorter title for section on suppressing raw outputs (with <>)

• reorder topics: show raw python objects first, then the 3 tags-related sections

• subsection on setting a cell tag is made a simple admonition

• also mention myst build -execute --html - following an exchange on discord the other day

another micro typo made it in the mix