Deprecate the --force-gomod-tidy CLI flag

[eskultety]

Running go mod tidy on the input source repository will result in dirtying the repo which is likely an undesirable effect that we should avoid doing. On the other hand, if we keep the flag and start running all operations on a temporary working copy of the repository the effect of the flag will be discarded with the working copy at the end of fetch-deps which may confuse our user base.

The good thing is that we even documented (https://github.com/containerbuildsystem/cachi2/blob/main/docs/gomod.md#--force-gomod-tidy) the flag as questionable, warning users it may be dropped in the future. The time has come now that we should improve our game and mandate a temporary working copy of the input repository for all pkg mgr backends.

Blocks:

• Cachi2 prefetching is making changes on a Go project's source #707
• Cachi2 prefetching is making changes on a source #712