feature #9394 Adding Code of Conduct (egircys)

This PR was submitted for the master branch but it was squashed and merged into the 2.7 branch instead (closes #9394).

Discussion
----------

Adding Code of Conduct

Adding the Contributor Covenant Code of Conduct version 1.4.
Relates to symfony/diversity#1

**TODO**
- [x] Add the link to the enforcement team page
- [x] Add the link to the enforcement process
- [x] Add the link to concrete real-world examples of unwanted behavior
- [x] Change "Project maintainers" to "Enforcement team members"

Part of #9340 and #9393

Replaces symfony/symfony#24896

Commits
-------

02e4860 update contributor covenant link & documents fix
2de768f change project team to enforcement team
0e7b539 add link to core team
e61a403 Replace ethnicity with ethnic origin
2f8aa5d Change "race" to "ethnic origin"
1b0e633 Change "project's leadership" to "core team"
464ea45 add link to examples document
eba3ecf Adding Code of Conduct

contributing/code_of_conduct/index.rst

@@ -0,0 +1,92 @@
+Code of Conduct
+===============
+
+Our Pledge
+----------
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnic origin, gender identity and expression, level of experience,
+education, socio-economic status, nationality, personal appearance,
+religion, or sexual identity and orientation.
+
+Our Standards
+-------------
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+  advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+Our Responsibilities
+--------------------
+
+:doc:`Enforcement team members </contributing/code_of_conduct/enforcement_team>`
+are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Enforcement team members have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+Scope
+-----
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by enforcement team members.
+
+Enforcement
+-----------
+
+Instances of abusive, harassing, or otherwise unacceptable behavior 
+:doc:`may be reported </contributing/code_of_conduct/reporting_guidelines>`
+by contacting the :doc:`enforcement team members </contributing/code_of_conduct/enforcement_team>`.
+All complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. The enforcement team is
+obligated to maintain confidentiality with regard to the reporter of an incident.
+Further details of specific enforcement policies may be posted separately.
+
+Enforcement team members who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by the
+:doc:`core team </contributing/code/core_team>`.
+
+Attribution
+-----------
+
+This Code of Conduct is adapted from the `Contributor Covenant`_, version 1.4,
+available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+
+Related Documents
+-----------------
+
+.. toctree::
+    :maxdepth: 1
+
+    reporting_guidelines
+    enforcement_team
+    concrete_example_document
+
+.. _Contributor Covenant: https://www.contributor-covenant.org