fix: install devtools plugin only after app is created and installed (#1063)

[popov-a-e]

Closes #1063

Turned out in nuxt plugin environment, pinia._a is not yet defined which resulted in devtools unable to find app record.

[netlify]

✅ Deploy Preview for pinia-official canceled.

Name	Link
🔨 Latest commit	9ea96a4
🔍 Latest deploy log	https://app.netlify.com/sites/pinia-official/deploys/62b767aeaee0a700094b0c47

[posva]

Thanks for the PR but this completely changes the behavior of plugins. The fix should be possible with minimal changes and without changing how stores are initialized

[popov-a-e]

OK, I ended up applying same logic to devtools plugin only.
Tests checked.

[popov-a-e]

@posva Hi Eduardo, is it OK now?

[posva]

Thanks but we really want to avoid adding any new hook like this.
Instead, let's move this kind of logic to the devtools: if the registerPiniaDevtools() haven't been called yet, we buffer the pending stores and once the devtools are registered, we add the store to the devtools.