Add include_in_rss field to Post

[yakky]

Description

Field is used to filter posts to be visible in the rss feed

References

Fix #663

Fix #690

Checklist

• [x] I have read the contribution guide
• [x] Code lint checked via inv lint
• [x] changes file included (see docs)
• [x] Usage documentation added in case of new features
• [x] Tests added

[github-actions[bot]]

Coverage: 97.086% (+0.09%) from 97.001% when pulling b8125c274c267a5b9ce6fad1df42367f82d96e2a on feature/issue-663 into c6f85dffc8ff0e22aafd8a1bc61e162f1de5a4e3 on develop.

[github-actions[bot]]

Coverage: 96.954% (-0.05%) from 97.001% when pulling b8125c274c267a5b9ce6fad1df42367f82d96e2a on feature/issue-663 into c6f85dffc8ff0e22aafd8a1bc61e162f1de5a4e3 on develop.

[codecov[bot]]

Codecov Report

Patch coverage: 85.71% and project coverage change: -0.04 :warning:

Comparison is base (c6f85df) 94.26% compared to head (ece87e6) 94.22%.

:exclamation: Current head ece87e6 differs from pull request most recent head b8125c2. Consider uploading reports for the commit b8125c2 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #728 +/- ## =========================================== - Coverage 94.26% 94.22% -0.04% =========================================== Files 26 26 Lines 1813 1819 +6 Branches 260 260 =========================================== + Hits 1709 1714 +5 - Misses 52 53 +1 Partials 52 52 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `94.22% <85.71%> (-0.04%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/nephila/djangocms-blog/pull/728?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila) | Coverage Δ | | |---|---|---| | [djangocms\_blog/admin.py](https://codecov.io/gh/nephila/djangocms-blog/pull/728?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila#diff-ZGphbmdvY21zX2Jsb2cvYWRtaW4ucHk=) | `83.06% <ø> (ø)` | | | [djangocms\_blog/managers.py](https://codecov.io/gh/nephila/djangocms-blog/pull/728?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila#diff-ZGphbmdvY21zX2Jsb2cvbWFuYWdlcnMucHk=) | `92.50% <80.00%> (-0.55%)` | :arrow_down: | | [djangocms\_blog/feeds.py](https://codecov.io/gh/nephila/djangocms-blog/pull/728?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila#diff-ZGphbmdvY21zX2Jsb2cvZmVlZHMucHk=) | `85.03% <100.00%> (ø)` | | | [djangocms\_blog/models.py](https://codecov.io/gh/nephila/djangocms-blog/pull/728?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila#diff-ZGphbmdvY21zX2Jsb2cvbW9kZWxzLnB5) | `98.01% <100.00%> (+<0.01%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nephila)

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