Template repeated Dockerfiles in knobots/actions

Several Dockerfiles under knobots/actions contain the same TODO comment:

`# TODO: figure out how to template this.`

These include:
knobots/actions/update-deps/Dockerfile
knobots/actions/update-gofmt/Dockerfile
knobots/actions/update-misspell/Dockerfile
knobots/actions/update-actions/Dockerfile

Each of these Dockerfiles is quite similar: using the same base image, structure, and commands and this TODO seems to suggest that these files could eventually be generated or templated to reduce repetition.

Compare knobots/actions/update-deps/Dockerfile, update-gofmt/Dockerfile, update-misspell/Dockerfile, and update-actions/Dockerfile to document their shared base image, structure, commands, and TODO. Research how this repository could generate or template these files; done should mean the repeated Dockerfile content is reduced through a clearly defined approach.

Written by the indexing model from the issue text.