Fix: uudoc manpage for individual utilities has wrong name (nit)

[shayelkin]

(I'd create an issue, but I think this is really too much of a nit).

When running uudoc manpage <utility> for any utility that isn't coreutils, the resulting manpage lists the command name as uudoc.

This is because uu_app() functions sets Command::name to uucore::util_name(), which unless we've set utility_is_second_arg first, would be the executable name rather than the utility name.

(Head of) output of uudoc manpage ls before this change:

.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.TH uudoc 1  "uudoc (uutils coreutils) 0.3.0"
.SH NAME
uudoc \- List directory contents.
Ignore files and directories starting with a \*(Aq.\*(Aq by default
.SH SYNOPSIS
\fBuudoc\fR

And after:

.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.TH ls 1  "ls (uutils coreutils) 0.3.0"
.SH NAME
ls \- List directory contents.
Ignore files and directories starting with a \*(Aq.\*(Aq by default
.SH SYNOPSIS
\fBls\fR 

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)