Add hexamine to camping item groups

[starlightsys]

Makes hexamine less rare by adding it to camping related item groups.
references #25239

Summary

SUMMARY: Content "Makes hexamine less rare by adding it to camping related item groups."

Purpose of change

As discussed in #25239, some explosives related recipes are very challenging to find components for. This change makes hexamine simpler to come by, by adding it to camping related item groups, as it is sometimes used as a camping fuel.

Describe the solution

This adds chem_hexamine as a rare drop for the college_camping, camping andallsporting item groups.

Describe alternatives you've considered

Adding an item for hexamine camping fuel tablets which can be disassembled into hexamine or a Cooking craft for purified hexamine, but seeing as the flavor text for chem_hexamine mentions them as waxy camping fuel tablets, I abandoned those ideas.

Additional context

[starlightsys]

Are there changes I should make to ensure that the CI builds pass?

[kevingranade]

No, it is currently suffering from an outage in a build dependency. We'll have to either wait for it to clear up, or find a new server to pull the dependencies from.