CLI: New dotenv output format

[cimnine]

I would appreciate it if the GitVersion CLI could output all the variables in dotenv format:

$ dotnet gitversion -output dotenv
AssemblySemFileVer=1.0.1.0
AssemblySemVer=1.0.1.0
BranchName=main
BuildMetaData=
CommitDate=2024-08-21
CommitsSinceVersionSource=0
…

This would allow more simplified CI/CD jobs with the two most important CI systems, GitLab CI and GitHub Actions. Both allow to pass environment variables to other jobs by writing them to a specific file (as documented for GitLab and GitHub). The first step of the pipeline would calculate the GitVersion-variables and export them, and all subsequent jobs could use those variables.

One important thing to consider is what to do with null values. In the example above, BuildMetaData is null. If it's in the output, the environment variable will be defined as empty. But most probably, all GitVersion-variables that are null should not be printed at all in dotenv mode.

[arturcic]

I think it's a nice suggestion, so I will create an issue out of it