feat: add editorconfig

[mateusoliveira43]

Description

Add editorconfig to project. This will check all project's file format, by checking:

• if there is no trailing whitespace in them
• if there is a empty newline at the end of them
• if they use the correct indent style (tab or space)
• if they have correct indent size

How to test

Run make ec

[kaovilai]

For .go

Indentation
We use tabs for indentation and gofmt emits them by default. Use spaces only if you must.

https://go.dev/doc/effective_go#formatting

[kaovilai]

Why not leave .go files out of editorconfig and do something like
openshift/oadp-operator#1337

[mateusoliveira43]

did not understand the linked PR

but yes, go files and Makefile both accept tabs and spaces (go example of spaces: the headers copyright), so added them to list of indent_style=unset. go fmt (run by golangci-lint) will take care of this for us in go files

[kaovilai]

The tab character is a very important part of the syntax of Makefiles.

So Makefile should not be indented using spaces. Yes unset sounds good.

Spaces can exists in go and makefile but not as an indent method for non-comments.