Add the accumulate filter (#9133)

* Add the accumulate filter

- Add myself as a maintainer for it.
- Some integration tests.

* accumulate: fix documentation and add test aliases

The aliases file was copied over from
tests/integrations/targets/filter_dict/aliases as the documentation[1]
suggests to use the same group as existing similar tests.

[1]: https://docs.ansible.com/ansible/latest/dev_guide/testing/sanity/integration-aliases.html

Suggested-by: Felix Fontein <felix@fontein.de>

* accumulate: documentation: markup consistency with other plugins

Suggested-by: Felix Fontein <felix@fontein.de>
Suggested-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

* filter/accumulate: Validate input is a Sequence

Accepting arbitrary iterables might lead to surprising behavior so we
are stricter on what we accept in the filter.
Relaxing those requirements is easier than retrofitting them, in terms
of backwards compatibility.

Suggested-by: Felix Fontein <felix@fontein.de>
Signed-off-by: Max Gautier <mg@max.gautier.name>

* filter/accumulate: Document the behavior with a string

Signed-off-by: Max Gautier <mg@max.gautier.name>

---------

Signed-off-by: Max Gautier <mg@max.gautier.name>

tests/integration/targets/filter_accumulate/aliases

@@ -0,0 +1,5 @@
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+azp/posix/3

tests/integration/targets/filter_accumulate/tasks/main.yml

@@ -0,0 +1,35 @@
+---
+# Copyright (c), Max Gautier <mg@max.gautier.name>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+- name: Filter | Accumulate | Test valid values
+  assert:
+    that:
+      - "'abc' | community.general.accumulate == ['a', 'ab', 'abc']"
+      - "['a', 'b'] | community.general.accumulate == ['a', 'ab']"
+      - "[1, 2, 3] | community.general.accumulate == [1, 3, 6]"
+      - "[['foo'],['bar'],['foobar']] | community.general.accumulate == [['foo'], ['foo', 'bar'], ['foo', 'bar', 'foobar']]"
+      - "'path/to/file' | split('/') | map('split', '/') | community.general.accumulate | map('join', '/') == ['path', 'path/to', 'path/to/file']"
+      - "[{'foo':1}, {'bar':2}] | map('dict2items') | community.general.accumulate | map('items2dict') == [{'foo':1}, {'foo':1, 'bar':2}]"
+
+
+- name: Filter | Accumulate | Test invalid values | Integer
+  debug:
+    var: "1 | community.general.accumulate"
+  register: integer_result
+  ignore_errors: true
+
+- name: Filter | Accumulate | Test invalid values | Non uniform list
+  debug:
+    var: "['aa', 1] | community.general.accumulate"
+  register: non_uniform_list_result
+  ignore_errors: true
+
+- name: Filter | Accumulate | Test invalid values | Check errors
+  assert:
+    that:
+      - integer_result is failed
+      - integer_result.msg is match('Invalid value type.*')
+      - non_uniform_list_result is failed
+      - non_uniform_list_result.msg is match('Unexpected templating type error.*can only concatenate str.*')