Bump versions for sessions keys migration

[s0me0ne-unkn0wn]

Fixes #262

CC @bkchr

• Does not require a CHANGELOG entry

[kianenigma]

It is an interesting tie to safeguard a migration to a specific spec version. But the downside is that an emergency upgrade like 1.1.2 can disrupt the flow :)

Somewhat more ideally, a migration would be smart enough to know if it is executed or not. In some migrations, this is possible, in some it is harder but can be achieved if we attach a unique identifier to all impls of OnRuntimeUpgrade and then we will never have to worry about duplicate or stale migrations again.

[bkchr]

Ty!

[bkchr]

@kianenigma paritytech/polkadot-sdk#2421

[s0me0ne-unkn0wn]

@kianenigma yes, exactly. The root cause of the problem is that some runtime structures, as SessionKeys, are not versioned. We should either make them versioned or implement something like what you're talking about (we have paritytech/polkadot-sdk#2421 for that), but until then we have no options but use this hacky and brittle way 🤷

[bkchr]

/merge

[ggwpez]

It would be safer to create a storage key like :upgrade_session_keys_migration_executed and then manually cleaning it up via governance afterwards.