Dvc

* tests: cover run cache with functional tests (4018) skshetry
* plots: fix a couple of bugs (4017) Suor
* RepoTree: work with dirty repos (4005) efiop
* run: use -f/--force to overwrite, fix msg (4011) skshetry
* plots modify: do not convert output types to plot on unset (4009) skshetry
* dvc.yaml: preserve meta (4008) skshetry
* plots modify: complain if template does not exist (3995) skshetry
* add/run/import-url: don't use -f as --file (4004) efiop
* plots: rename --no-csv-header to --no-header (4001) efiop
* config/remote/cache: make --system/--global/--local mutually exclusive (4000) efiop
* status: introduce --show-json (3998) efiop
* snap: build fixes (3990) casperdcl
* Refactor plots (3994) Suor
* plots: find metric data in yaml dictionary (3992) pared
* stage: don't consider stage as cached if checksum/cmd changed (3993) skshetry
* tests serializing of stage to lockfile (3988) skshetry
* tests: serialize pipeline file (3985) skshetry
* plots: fix help message (3983) efiop
* remove unnecessary dependencies (3987) skshetry
* tests: update mock ssh server (3986) skshetry
* remote: tree: don't ignore exceptions (3977) efiop
* log: show modifying if entry already exists in dvcfile (3978) skshetry
* tests: StageLoader for Pipeline file stages (3976) skshetry
* issue template: do not auto-add labels on new issues (3979) skshetry
* Fix loading of params from run cache (3972) skshetry

* pyinstaller: add hook for google-api-python-client (3965) efiop
* snap: restrict site-package checks (3878) casperdcl
* Subcommand help (3956) aerubanov
* remote: fix remaining gdrive build issues (3959) pmrowla
* remote: fix build errors (3957) pmrowla
* refactor/test multistage load for params and outputs (3949) skshetry
* Unify metrics behavior with dirs (3935) nik123
* remote: finish separating RemoteTree methods (3946) pmrowla

* tests: move mock-ssh-server git dependency (3953) efiop
* plots: completion/spelling fixups (3952) efiop
* tests: gdrive: don't cache url (3941) efiop

* Rename --xlab to --x-label, X_TITLE to X_LABEL, same for y (3948) Suor
* plots: fix error when there are no plots in repo (3940) efiop
* dvc: require `--external` for external outputs (3929) efiop
* remote: separate tree functions from main remote classes (3931) pmrowla
* remote: modify: fix --unset (3939) efiop
* Fix quadratic behavior in Repo._collect_stages() (3932) Suor

* dvc: remove `dvc metrics add/remove` (3928) efiop
* refactor: rename utils.stage to utils.yaml (3923) skshetry
* Fix modifying plot (3926) Suor
* bugfix: rerun stage when command is changed (3922) skshetry
* dvc: replace `pipeline` with `dag` (3905) efiop
* Implement removing of the stage (3881) skshetry
* dvc: rename "working tree" to "workspace" (3914) efiop
* dvc: rename `dvc lock` -> `dvc freeze` (3915) efiop
* Add plots props and `plots modify` params (3911) Suor
* use fork of mockssh-server (3910) skshetry
* pre-commit: don't run dvc in parallel (3912) efiop
* use `selectors` instead of `select.select()` (3899) skshetry
* Update bug report template (3903) jorgeorpinel
* tests: make ssh_server session scoped (3898) efiop
* dvcignore: use correct root .dvcignore for subrepos (3895) pmrowla
* plots: replace --show-json with --show-vega (3891) efiop
* Bugfix: _credentials_location (3896) nickdelgrosso
* brancher: only yield git revisions that contain repo_root (3883) pmrowla
* modify issue template (3887) skshetry

* dvcignore: fix bug in subrepo detection (3880) efiop
* run: raise error when command is not specified (3850) skshetry
* ignore: CleanTree should always check ignores, not just for walk() (3876) pmrowla
* addressing: allow stage name addressing without ":" (3842) skshetry
* run-cache: don't forget to set wdir (3873) efiop
* state: always use working trees (3871) pmrowla
* log: reduce log, make it readable/easier (3834) skshetry