add instructions to checkout the correct tag

[cgardens]

What

• docker-compose up leads to a broken state right now.
• issue described here: Document Release Story #1049
• versions of connectors have been updates. but docker-compose up runs whatever the core containers were when the last release happened. the issue is that the new connector versions aren't compatible with those old version anymore (catalog updates and secrets changes).

How

• this is a stop gap until we decide how we want to resolve the issue mentioned above. this is enough to get us to a non-broken state. The alternative can be found in this draft pr: revert connectors in index back to what they were at release time #1050, but i think it is a worse hack to get this fixed. I am going to merge this as soon as the build passes as a hotfix.

[michel-tricot]

Shouldn't we do

git checkout tags/$(cat .env | grep VERSION | cut -d = -f 2)

[michel-tricot]

I am a bit surprised by the need for that change.

I thought we didn't rely on the state of the repo when doing a docker compose up. It should only use published images doesn't it?

[cgardens]

I reverted this. This was wrong; I was temporarily confused.