Load prescribed versions of GAP packages

[ThomasBreuer]

When GAP.jl gets loaded by (for example) Oscar.jl, it is necessary to control which versions of GAP packages get loaded.
For example, silently loading newer versions than available in the distributed GAP can yield different test results.
(An example is discussed in oscar-system/Oscar.jl/pull/3444.)

Thus we need a way to state before GAP gets started which GAP package versions are needed, and then this information must be used before GAP autoloads its packages.

Alternatively, we could start GAP without autoloaded packages, and provide a Julia function for loading a list of packages (with prescribed version numbers) in the same way as GAP does it, that is, GAP decides about the order in which these packages will get loaded.