Guide users on what to do next if nothing was found in a search

When a new or relatively nontechnical user uses Discover to search for
an app they know exists (like VLC, or Chrome, or TeamViewer) which just
happens to not be in any configured repos due to distro packaging
policies or lack of packaging resources, Discover says "Nothing found"
and the user is left thinking one of two things:

"Man, Discover sure is stupid, it can't even find $APP!"

"Wow, this Linux thing sucks, they don't even have $APP!"

Neither is true, but by not showing the user the app they expect,
Discover inadvertently creates these impressions in their minds,
because they are not familiar with the concept of divergent and
political distro packaging policies--and frankly, they probably don't
care. As a result, Discover and KDE look stupid, and FOSS environments
are tarnished in the user's mind. This user knows that the app in
question exists, and they want to use it, so what are they going to do
next? Search the web for it, just like they did on Windows or macOS,
which is where they found it last time they needed to install it.

This commit attempts to improve the situation by having Discover show
an extended message that helps to explain the situation in this case,
and directs users to the web with a helpful button they can click on
to perform a DuckDuckGo search for "Linux $SEARCH_TERM". This
accomplishes several things:

1. It helps the user understand that Discover isn't at fault here
2. It blame-shifts the problem onto distros
3. It makes Discover seem helpful and friendly for assisting the user in
   doing what they were going to do next anyway (search the web for it)
4. It provides a warning that apps found on the web are more risky than
   apps in repos, as a simple CYA
5. Introduces the concept of a non-Google search engine, planting the
   seed in the user's mind that it's possible to search the web without
   Google, in case they didn't already know this
2 jobs for help-users-find-software-outside-the-repos in 14 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Build
failed freebsd_qt515 #142403
FreeBSD

00:00:11

failed suse_tumbleweed_qt515 #142402
Linux

00:00:12

 
Name Stage Failure
failed
suse_tumbleweed_qt515 Build
ERROR: No files to upload                          
Uploading artifacts...
WARNING: CoberturaLcovResults.xml: no matching files
ERROR: No files to upload
Uploading artifacts...
WARNING: cppcheck.json: no matching files
ERROR: No files to upload
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
freebsd_qt515 Build
    raise Exception("Unable to locate requested dependency in the registry: {} (branch: {})".format( identifier, branch ))
Exception: Unable to locate requested dependency in the registry: kuserfeedback (branch: @stable)
Uploading artifacts for failed job
Uploading artifacts...
Runtime platform
arch=amd64 os=freebsd pid=66869 revision=8925d9a0 version=14.1.0
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit status 1