Standard way to initialize a pallet after genesis

[kianenigma]

in the future probably would be nice to have an initialize function coming from the pallet itself.

Originally posted by @shawntabrizi in paritytech/polkadot#5582 (comment)

Currently, we can easily initiate a pallet in the runtime by using on_runtime_upgrade. This is fine, but we can dp better and create a standard process for this.

Also, in the academy, we realized that the students are quite confused about this and mistakenly think that genesis_build is called upon creation of the pallet, not creation of the whole runtime.

[kianenigma]

duplicate of #8373