It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
This allows text editors to use correct syntax coloring for the heredoc sections.
Heredoc tag names we use:
languages: SQL, JS, RUBY, LUA, HTML, CSS, SCSS, SH, HBS, XML, YAML/YML, MF, ICS
other: MD, TEXT/TXT, RAW, EMAIL
New range tag for local dates with syntax like:
```
[date-range from=2022-01-06T13:00 to=2022-01-08 timezone=Australia/Sydney]
```
Previously, 2 dates in one line were considered as range. It was hard to decide if 2 dates are range when they were in separate lines or have some content between them.
New explicit tag should clearly distinguish between single date and range.
Common code from `addLocalDate` is extracted to `addSingleLocalDate`.
Both `addLocalDate` and new `addLocalRange` are using `addSingleLocalDate`.
Also, `defaultDateConfig` was extracted to have one place for all possible parameters.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
