[FEAT] add "main" tag that builds bleeding-edge version

[axiopaladin]

Is this a new feature request?

• I have searched the existing issues

Wanted change

The "latest" tag gives the latest stable version of Transmission. Please add another tag (suggested name "main", after the primary branch of the base Transmission repo) that gives the nightly build of the very newest code.

Reason for change

Sometimes users want to try out features that haven't been released in a stable version. For example, 4.1.0 will have sequential downloading, and this feature is included and working in the
"main" development branch, but it was not merged before 4.0.6 (the current stable) was released.

Proposed code change

Ideally this would be built from source via CI/CD, but if compiling from source is too much to ask then an alternative would be to grab necessary artifacts from the latest pre-release tag in the base Transmission repo's releases.

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