[Dockerhub] provide "fixed major, latest minor" containers

### Is your proposal related to a problem?

I want to be able to use a 2.6.x container, regardless of the x

### Describe the solution you'd like

`docker pull hasura/graphql-engine:v2.6.cli-migrations-v2`

Note that timescaledb already does something like that

`docker pull timescale/timescaledb-ha:pg14.2-ts2.6.1-latest`

can also be

`docker pull timescale/timescaledb-ha:pg14.2-ts2.6-latest`

Start by locating the Docker Hub image publishing and tag-generation workflow for graphql-engine, then compare its current tags with the requested fixed-major, latest-minor format and the TimescaleDB examples in the issue. Done means the requested v2.6 tag resolves to the appropriate container image and the behavior is verified for the relevant image variant.

Written by the indexing model from the issue text.