I want to try using postgress source with 10K fetch size as it is slow with large tables. can somebody with access help me: • create a custom branch and merge this PR into a custom branch • build a custom source-postgress image so I can try that?

you can do this locally as well. Clone the repository, change the params, do a docker build and push it to a public docker hub and in the settings of the webapp you can use this custom connector

I thougth I can only change image tag in the UI. can I give it a full docker address?

yup

use the new connector option

there you can provide a full URI