feat: Add support for PHP 8.1, 8.2

[dplewis]

New Pull Request Checklist

• [x] I am not disclosing a vulnerability.
• [x] I am creating this PR in reference to an issue.

Issue Description

Migrate TravisCI to Github Actions

Closes: https://github.com/parse-community/parse-php-sdk/issues/479, https://github.com/parse-community/parse-php-sdk/issues/488

Approach

• Support PHP 8.1, 8.2
• Drop support for <= 8.0
• Remove travis
• Bump composer packages
• Remove mailgun adapter
• Remove warnings
• Remove deprecation warnings
• Support for Parse Server 6
• Fix flaky tests
• Add documentation deployment

TODOs before merging

• [x] Add tests
• [x] Add changes to documentation (guides, repository pages, in-code descriptions)
• [x] Add changelog entry

[parse-github-assistant[bot]]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.20 :warning:

Comparison is base (184460b) 98.07% compared to head (86df298) 97.88%.

:exclamation: Current head 86df298 differs from pull request most recent head 57b8d4f. Consider uploading reports for the commit 57b8d4f to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #489 +/- ## ============================================ - Coverage 98.07% 97.88% -0.20% - Complexity 1063 1066 +3 ============================================ Files 39 39 Lines 2964 3262 +298 ============================================ + Hits 2907 3193 +286 - Misses 57 69 +12 ``` | [Impacted Files](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community) | Coverage Δ | | |---|---|---| | [src/Parse/ParseUser.php](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-c3JjL1BhcnNlL1BhcnNlVXNlci5waHA=) | `98.40% <ø> (+0.09%)` | :arrow_up: | | [src/Parse/HttpClients/ParseCurlHttpClient.php](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-c3JjL1BhcnNlL0h0dHBDbGllbnRzL1BhcnNlQ3VybEh0dHBDbGllbnQucGhw) | `95.50% <100.00%> (+0.15%)` | :arrow_up: | | [src/Parse/HttpClients/ParseStreamHttpClient.php](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-c3JjL1BhcnNlL0h0dHBDbGllbnRzL1BhcnNlU3RyZWFtSHR0cENsaWVudC5waHA=) | `96.10% <100.00%> (-2.53%)` | :arrow_down: | | [src/Parse/ParseACL.php](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-c3JjL1BhcnNlL1BhcnNlQUNMLnBocA==) | `100.00% <100.00%> (ø)` | | | [src/Parse/ParseQuery.php](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community#diff-c3JjL1BhcnNlL1BhcnNlUXVlcnkucGhw) | `99.52% <100.00%> (-0.24%)` | :arrow_down: | ... and [18 files with indirect coverage changes](https://codecov.io/gh/parse-community/parse-php-sdk/pull/489/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=parse-community) 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=parse-community). 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=parse-community)

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[mtrezza]

Changed this PR to feat since it changes the supported PHP versions and is therefore a breaking change.

[mtrezza]

@dplewis Do you remember how to prepare and publish a release in this repo?

Past commits to prepare releases only contain the changelog entry and bumping the internal client version that is sent to Parse Server in ParseClient.php.

For example https://github.com/parse-community/parse-php-sdk/commit/fa132ca2c35d8e405b1a3363b1e0efafe3851e49

We don't have auto-release in this repo yet. To add that, I'd like to understand the steps needed to publish it manually.

[dplewis]

@mtrezza I have absolutely no idea how to publish this or how it works. I just do a tag and release and it magically publishes. @montymxb @acinader handled releases So they might know

[mtrezza]

I've opened https://github.com/parse-community/parse-php-sdk/issues/492 to find out more about release publishing.