CLI flag for running container as the current user

[kponichtera]

Closes #3498

- What I did

I’ve added the --current-user boolean flag to the docker run command to avoid docker run -u $(id -u):$(id -g) construct which often appears in the scripts that use Docker containers for development.

- How I did it

The user parameter of the Docker API call is now built by the dedicated parseUser function in opts.go file. It checks if --current-user flag was set. In such case, it fetches current user UID and GID using Go’s standard library, builds the string UID:GID, and passes it to the Docker API. The --user flag has precedence over --current-user - if both are specified, the --user one will be taken.

There is also a unit test, which verifies the behavior of the function that builds the API call user field. I’ve also updated bash and zsh autocompletion files, as well as the Markdown reference document for the run command.

If there are some things that should be done and which I missed, please let me know and I will address them.

- How to verify it

1. Build repo with docker buildx bake
2. Run ./build/docker run -it --current-user ubuntu /bin/bash - the Ubuntu container will run the process inside with the same UID and GID as the CLI caller’s process.
3. Run ./build/docker run -it --current-user -u 1234:1234 ubuntu /bin/bash - the -u flag will take precedence

- Description for the changelog

Added --current-user flag to the docker run command.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Merging #3499 (dea9b89) into master (e1d4324) will increase coverage by 0.00%.
The diff coverage is 78.57%.

@@           Coverage Diff           @@
##           master    #3499   +/-   ##
=======================================
  Coverage   59.01%   59.02%           
=======================================
  Files         284      284           
  Lines       23833    23846   +13     
=======================================
+ Hits        14066    14076   +10     
- Misses       8908     8910    +2     
- Partials      859      860    +1     

[kponichtera]

I have modified the code and implemented the suggestion, mentioned in #3498. Instead of new --current-user flag, running the container as current user is now done though setting already existing --user flag to value current.

[albers]

Please see the recent discussion in #3498 (comment)

[kponichtera]

@albers Looking at the discussion in #3498 it seems like a dedicated --current-user flag would be a better solution than trying to find a safe value for the --user one. Should I revert this PR to state with the --current-user flag?

[albers]

Should I revert this PR to state with the --current-user flag?

I think, yes.
@thaJeztah @ndeloof WDYT?