doc: interpret-trailers: convert to synopsis style

doc: interpret-trailers: convert to synopsis style

See e.g. 0ae23ab5 (doc: convert git worktree to synopsis style,
2025-10-05) for the markup rules for this style.

There aren’t many subtleties to the transformation of this doc since it
doesn’t use any advanced constructs. The only thing is that "`:`{nbsp}" is
used instead of `': '` to refer to effective inline-verbatim with
a space (␠).[1] I also use (_) for emphasis although (') gives the
same result.

Also prefer linking to Git commands instead of saying e.g. `git
format-patch`. But for this command we can type out git-interpret-
trailers(1) to avoid a self-reference.

Also replace camel case `<keyAlias>` with kebab case `<key-alias>`.
And while doing that make sure to replace `trailer.*` with
`trailer.<key-alias>`.

† 1: Similar to "`tag:`{nbsp}" in `Documentation/pretty-formats.adoc`

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>