Replace postgresql 14+ function with postgresql 12 compatible function

[reductionista]

This included a function which only works with postgresql 14+, but we must support versions 12-15. Updating with a replacement that will work on 12+

Update: this doesn't use a direct key on the 7 columns in part because that would result in a very large index, and in part because NULL's add some additional complexity anyway. In postgresql 12 & 13, we have to define a helper function for the IMMUTABLE property, in 14 there is a builtin helper to do this.

[github-actions[bot]]

I see that you haven't updated any CHANGELOG files. Would it make sense to do so?

[reductionista]

Does this help? https://github.com/smartcontractkit/chainlink/pull/12155

Yes it does, thank you!

[cl-sonarqube-production[bot]]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[reductionista]

LGTM!

Thanks! Giving @mateusz-sekara one more chance to look at it before it gets merged, in case he still has concerns. If not, will merge this tomorrow.