Upgrade gopls to v0.19.0, add make fix

[silverwind]

Upgrade to v0.19.0 and fix issues. Runs with new warning serverity setting. This likely does less checks than before. Additionally, add make fix which runs modernize. This is also verified on CI.

For the record, here are the issues discoverd when running with info severity, in case we want to fix these:

tests/integration/repo_test.go:95:5-14: could use tagged switch on i
tests/integration/api_packages_generic_test.go:149:4-64: could use tagged switch on setting.Packages.Storage.Type
services/webhook/msteams_test.go:33:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:59:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:85:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:111:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:138:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:161:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:187:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:213:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:239:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:266:4-33: could use tagged switch on fact.Name
services/webhook/msteams_test.go:407:4-33: could use tagged switch on fact.Name
tests/integration/api_packages_conan_test.go:350:6-33: could use tagged switch on pf.Name
models/issues/tracked_time_test.go:98:3-18: could use tagged switch on user.ID
tests/integration/api_token_test.go:505:5-43: could use tagged switch on minRequiredLevel
services/gitdiff/gitdiff.go:220:33-46: method "getLineLegacy" is unused

[silverwind]

BTW the modernize fixer seems quite fast, make fmt completes in 10 seconds on my machine.

[silverwind]

Oh and by the way I'm not completely sold that fmt should also perform code fixes. Maybe it's better to split this out into a make fix target or similar.

[silverwind]

Decided to split into separate make fix target for automated code fixes.