Replace `iroha2` with `iroha1` labels

[mversic]

Since we made iroha2 into main branch, I think we should remove iroha2 labels and create iroha1 labels. We will no longer tag new issues/PRs with iroha2 label if they are targeting main branch, but we will tag issues/PRs with iroha1 if they are targeting iroha1-main

Suggestion:

1. create new label iroha1
2. tag all issues/PRs related to iroha1 with iroha1 label
3. delete iroha2 label

this should be done in github and zenhub

[s8sato]

Just a thought, but for step 2, the following may be worth trying in an experimental repository:

gh [issue|pr] list --search "-label:iroha2" | (extract numbers) | xargs -I {} gh [issue|pr] edit {} --add-label "iroha1"

https://cli.github.com/manual/gh

[nxsaken]

Instead of deleting the iroha2 label, I renamed it to iroha2-dev. It shouldn't be used anymore: assume that new unlabeled issues/PRs are related to Iroha 2.