[Nexthop] Add a Distro Image demo container example

[travisb-nexthop]

Pre-submission checklist

• I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• pre-commit run

Summary

This adds an example of an other_dependency which creates and runs a custom container.

Here a simple clock service inside a container is added as this example.

Test Plan

Add this to the image manifest:

"other_dependencies": [
  { "execute": "examples/demo_container/build.sh" }
]

When the device boots, you can check the time:

[root@dut ~]# cat /var/clock/time.txt
  ________________________________________
| Current time is Thu Feb  5 18:34:43 2026 |
  ========================================
                                               \
                                                \
                                                 \
                                                  \
                                                     .-=-==--==--.
                                               ..-=="  ,'o`)      `.
                                             ,'         `"'         \
                                            :  (                     `.__...._
                                            |                  )    /         `-=-.
                                            :       ,vv.-._   /    /               `---==-._
                                             \/\/\/VV ^ d88`;'    /                         `.
                                                 ``  ^/d88P!'    /             ,              `._
                                                    ^/    !'   ,.      ,      /                  "-,,__,,--'""""-.
                                                   ^/    !'  ,'  \ . .(      (         _           )  ) ) ) ))_,-.\
                                                  ^(__ ,!',"'   ;:+.:%:a.     \:.. . ,'          )  )  ) ) ,"'    '
                                                  ',,,'','     /o:::":%:%a.    \:.:.:         .    )  ) _,'
                                                   """'       ;':::'' `+%%%a._  \%:%|         ;.). _,-""
                                                          ,-='_.-'      ``:%::)  )%:|        /:._,"
                                                         (/(/"           ," ,'_,'%%%:       (_,'
                                                                        (  (//(`.___;        \
                                                                         \     \    `         `
                                                                          `.    `.   `.        :
                                                                            \. . .\    : . . . :
                                                                             \. . .:    `.. . .:
                                                                              `..:.:\     \:...\
                                                                               ;:.:.;      ::...:
                                                                               ):%::       :::::;
                                                                           __,::%:(        :::::
                                                                        ,;:%%%%%%%:        ;:%::
                                                                          ;,--""-.`\  ,=--':%:%:\
                                                                         /"       "| /-".:%%%%%%%\
                                                                                         ;,-"'`)%%)
                                                                                        /"      "|
[root@dut ~]#