Dvc

* Move to yaml1.2 (4415) skshetry
* experiments: abstract executor output collection using trees (4402) pmrowla
* dvc: introduce merge-driver (4298) efiop
* git: handle rev_parse exception (4422) pmrowla

* experiments: fix flaky tests (4414) pmrowla
* tree: http: try GET on failed HEAD (4390) pared
* refactor: move toml/yaml serialization to dvc.utils.serialize (4411) skshetry
* status: check if target is missing both in cache and remote (4398) nik123
* metrics: show: debug info on parsing problems (4370) pared
* experiments: include experiment timestamps in `dvc exp show` output (4389) pmrowla
* upgrade to isort5 (4399) skshetry
* cleanup RepoTree (4405) skshetry
* Solve check-ignore broken in a Linux pipeline (4409) karajan1001
* update flake8 to latest version (4403) skshetry
* ui: '-j' option now mentions docs (4382) nik123
* tree: make get_hash return type and hash pair (4397) efiop
* tests: add .dvcignore on the tests expectations (4396) skshetry
* RepoTree: add support for subrepo traversal (4381) skshetry
* Derive WebDAVURLInfo from URLInfo instead of HTTPURLInfo (4391) iksnagreb
* outputs: validate that output is not ignored (4386) pared
* exception text: clarify error message (4339) bobertlo
* get-url: allow weak etag (4372) pared
* Solve result inconsistency of the DvcIgnoreFilter (4378) karajan1001
* experiments: add options to include/exclude columns in `exp show` (4375) pmrowla
* term: review "URL" term usage in remote cmds, and get/import-url (4364) jorgeorpinel
* Special dir warning 3436 (4229) aerubanov

* dvc: migrate to azure-storage-blob >= 12.0 (4379) efiop
* Remove dvcignore reset in `repo._reset` (4371) karajan1001
* check-ignore: update help output [qa] (4358) jorgeorpinel
* push: do not push .dir file for directory with missing files (4353) pmrowla
* Error message when no match found. (4354) karajan1001
* Config to enable/disable updater (4334) PuneethaPai
* Remove error message when exiting `--stdin` mode (4368) karajan1001
* pager: use --R/--RAW-CONTROL-CHARS with less (4369) pmrowla
* dvcignore: api to unhide subrepos directory (4324) skshetry

* Two new modes `--all` and `--stdin` for check-ignore (4323) karajan1001
* experiments: support `dvc repro --exp` command line params (4331) pmrowla
* repro: update status message for dvc-added files (4317) sarthakforwet
* config: use wtree for non-repo configs (4341) efiop
* import: fix importing into subdirectory bug (4340) pmrowla
* completion: bump shtab (4337) casperdcl
* experiments: add --no-pager option for `dvc exp show` (4345) pmrowla
* tests: fix regex (4329) skshetry
* updater: Remove unnecessary `(` in logging (4328) skshetry
* experiments: more intelligent checkout behavior (4320) pmrowla
* `dvc check-ignore` command (4282) karajan1001

* tree: don't save hash twice (4314) efiop
* Fix typo in `dvc remote modify` output (4311) arthurcgusmao
* remote: allow local options for repo remotes (4309) efiop
* tree: get rid of explicit tree arguments (4310) efiop

* Update pytest to >=6.0.1 (4308) skshetry
* commit: make sure deps/outs exist (4305) efiop
* dvc: fix --quiet mode (4304) efiop
* tree,remote: add support for WebDAV (4256) iksnagreb
* experiments: support local parallel execution in temp directories (4257) pmrowla
* Exclude pylint==6.0 (4300) skshetry