scripts: Rspamd stabilization pt. 2 (#3282)

* move modules adjustment file to new location

Because we link `/tmp/docker-mailserver/rspamd/override.d` to
`/etc/rspamd/override.d`, I think it makes sense to move the modules
adjustment file into `/tmp/docker-mailserver/rspamd/` as well.

I write the code in a way that it is backwards compatible for now, so
this is NOT a breaking change.

* minor improvement to `__rspamd__handle_user_modules_adjustments`

The expansion of `ARGUMENT3` is now done in a way that only adds the
whitespace in case the variable is set and not null.

* move test file structure to respect latest changes

Because we're now linking `rspamd/override.d/`, we can simplify the
setup a bit. But this requires a change in directory structure.

The current Rspamd test will be renamed to `rspamd_full.bats`, because I
plan on adding more tests in different files for different feature sets.
This is done to make this feature well-tested!

* improved and added tests to Rspamd-full

FYI: The line

```bats
_run_in_container grep 'sieve_global_extensions.*\+vnd\.dovecot\.pipe'
"${SIEVE_CONFIG_FILE}"
```

was testing a condition that should actually not be met, but when I
started working on this feature, I thought this was the correct
configuration. Adding the `assert_success` statements revealed this
wrong line.

I also added tests to check whether `override.d` is linked correctly.

* renamed: `rspamd.bats` => `rspamd_full.bats`

* added new tests for incomplete Rspamd feature set

We now test that warnings are emitted & features are disabled correctly.

* update documentation

test/config/rspamd_full/postfix-accounts.cf

@@ -0,0 +1,2 @@
+# password is 123
+user1@localhost.localdomain|{SHA512-CRYPT}$6$ARrjj74S83.7c53r$AZXMChav0r03LPEGAJJBmfUt59139rZ1zRIxrPhICSh.Y70Zjq6gClnF/cHDUG95dMoFt4Bkj6N4hvFSZ7L301