Better align with the `.editorconfig` files rules (_which `eclint` reads_).

Most of this is the upstream defaults and can be dropped.
- `SpaceAftertabs` (_possibly invalid name?_) was set to `true` but it doesn't appear any files covered rely on this. No context in `git blame` for it's addition, dropping.
- `Exclude` has a long history of pattern additions with minimal context. This is updated to be more specific now.
- `IgnoreDefaults` has been left for visibility. It could technically be set to `true`, but the SVG files should be ignored then.

`test/test-files/` is only ignored due to an upstream bug with `eclint` incorrectly detecting a file with the wrong encoding and triggering a failure as it's unsupported by `eclint`. Can be removed once a new release resolves that.

`test/bats/` and it's related submodules `bats-assert` / `bats-support` need to be ignored. In addition to not being relevant to the project, they supply their own `.editorconfig` with rules that seem to fail such as `max_line_length`.

`.git/` also isn't ignored by default (_it apparently was in an earlier version of `eclint` according to a bug report_).

We can bring the `indent_size = 2` rule into all files default. It helps establish a bit of consistency in the project files.

`.gitmodules` could possibly be ignored instead, it's also using tabs like `Makefile` so I've just configured that explicitly here.

The git submodules section doesn't seem relevant? Those changes shouldn't be committed, and we're not likely to modify those intentionally. The project supplies it's own `.editorconfig` file as root which would ignore this section, thus it's not really serving a purpose?

Most changes are for the `indent_size = 2` rule now having expanded relevance.

1 file needed a blank line `dovecot-master-accounts.md`, another had trailing white-space `mail_with_ldap.bats`.

Just white-space changes with indentation to be multiples of 2, and replace any tabbed indentation with spaces.

This has not been used since the switch to `supervisord`.