[packaging] Packaging updates

[tsmethurst]

This PR updates some of our packaging in the following ways:

1. Bump version of golang to 1.18.3.
2. Bump gotosocial-drone-build to 0.0.5 (which includes bumps to GoReleaser and Docker buildx).
3. Remove the bundled source tarball from releases, since it was misleading and unhelpful.
4. Add a release archive that just contains the bundled web/assets and web/templates folders, to make life easier for people doing ports.

Should close #654

However, it doesn't really address the 'tarbomb' point raised in that issue, because while you can instruct goreleaser to embed a root directory inside a tar, it would cause our installation instructions to change, and people would have to run different installation commands for different releases. This is not something that I like the idea of doing, so I left it out of this PR. However, if there's enough impetus and interest in changing this, we can still do this in another PR.

[igalic]

does this build the assets, too?

[tsmethurst]

does this build the assets, too?

Yes :) essentially it replaces that weird source tarball with a tar that just contains web/assets/dist and web/assets/template (so everything in the web/assets/ dir aside from the source dir). So when porting you can clone the latest tag, grab the compiled assets tar and untar it, then do whatever you need to do without having to install node/yarn