[Bank] Allow Bot Owner/Guild Owners to remove invalid users from the bank (#2845)

* Add command to remove dead members from bank

* Add a global check

* Added a FIXME so `bank_local_clean` is updated once bulk-update is implemented
Added a brief warning to warn devs not to use the `_get_base_group` as it can mess up their config files
Removed a redundant existence check

* Updated  commit to reflect changes requested in review

* Updated  commit to reflect changes requested in review

* 🤦

* Return command to run with user id so we don't worry about safeguarding the command agaisn't invalid formats

* Braaaainnn

Removed aliases that used old naming scheme

* TL:DR  Added global bank support, and rework permissions

Renamed `bank_local_clean` to `bank_prune`
Added support for global banks to `bank_prune`
`bank_prune` will now raise `BankPruneError` if trying to prune a local bank and `guild` is not supplied

Renamed `cleanup` subgroup to `prune`
`prune` subgroup will have 3 commands:
  `user`   :  Deletes the bank account for the specified member : Accepts `Union[discord.Member, discord.User, int]`
  `global` :  Prune global bank accounts for all users who no longer share a server with the bot
  `local`  :  Prune local bank accounts for all users who are no longer in the guild

Changed check for `prune` subgroup to be `@check_global_setting_admin()`
[p]bank prune local  : Can be run by Guild owners only
[p]bank prune global : Can be run by Bot Owner only
[p]bank prune user   : Can be run by Admins, Guild owners and Bot Owner

* Yikes ... Updated kwarg name

* Fixed unexpected unindent: docstring of redbot.core.bank.bank_prune:14:Field list ends without a blank line

* ...

* 3rd time lucky?

* 4th time lucky?

* Fix Docstring

* Initial commit to address review by Flame

* Updated code to reflect Flame's comments

* Skip pruning of unavailable guilds

* Fixed typo in string

* *sigh* black is the bane of my existence

* addressed Flames commends
Fixed [p]bank prune user, When run via DM it will now return an error message to the user (Thanks jack1142)

* Time to get some sleep

* 'DM' > 'DMs' in string

* Add towncrier entries

Signed-off-by: Draper <guyreis96@gmail.com>

* Update to reflect Flame's review

Signed-off-by: guyre <27962761+drapersniper@users.noreply.github.com>

redbot/core/config.py

@@ -883,6 +883,12 @@ class Config:
         self.custom_groups[group_identifier] = identifier_count
 
     def _get_base_group(self, category: str, *primary_keys: str) -> Group:
+        """
+        .. warning::
+            :code:`Config._get_base_group()` should not be used to get config groups as
+            this is not a safe operation. Using this could end up corrupting your config file.
+        """
+        # noinspection PyTypeChecker
         pkey_len, is_custom = ConfigCategory.get_pkey_info(category, self.custom_groups)
         identifier_data = IdentifierData(
             cog_name=self.cog_name,