[TECH DEBT] Deprecate Vault Modules

[garethgreenaway]

Description of the tech debt to be addressed, include links and screenshots

Deprecating all Vault functionality in Salt and moving it to:
https://github.com/saltstack/saltext-vault

First Salt version with Vault no longer present in the core: 3009.0

To be removed:

tests/pytests/functional/modules/test_vault.py
tests/pytests/integration/runners/test_vault.py
tests/pytests/integration/sdb/test_vault.py
tests/pytests/unit/runners/vault
tests/pytests/unit/runners/vault/test_vault.py
tests/pytests/unit/utils/test_vault.py
tests/pytests/unit/modules/test_vault.py
tests/pytests/unit/sdb/test_vault.py
tests/pytests/unit/pillar/test_vault.py
tests/integration/files/vault.hcl
salt/runners/vault.py
salt/utils/vault.py
salt/modules/vault.py
salt/modules/vault.py.off
salt/sdb/vault.py
salt/pillar/vault.py
salt/states/vault.py
doc/ref/runners/all/salt.runners.vault.rst
doc/ref/modules/all/salt.modules.vault.rst
doc/ref/sdb/all/salt.sdb.vault.rst
doc/ref/pillar/all/salt.pillar.vault.rst
doc/ref/states/all/salt.states.vault.rst