Prep for 4.1.5 release

[MGatner]

Updates changelog and version references for 4.1.5.

[kenjis]

It seems user_guide_src/source/changelogs/index.rst was updated when Prep for 4.1.2.
https://github.com/codeigniter4/CodeIgniter4/pull/4700/files#diff-381d2d09886543d18722e3aebb52071b41458d4659cc490ef63cb793d568b7e8

[kenjis]

I ran github_changelog_generator, but no CHANGELOG.md was generated.

$ docker run -it --rm -v "$(pwd)":/usr/local/src/your-app githubchangeloggenerator/github-changelog-generator --user codeigniter4 --project codeigniter4 --since-tag v4.1.4 --future-release v4.1.5 --token *****
Using these options:
:date_format=>"%Y-%m-%d"
:output=>"CHANGELOG.md"
:base=>"HISTORY.md"
:issues=>true
:add_issues_wo_labels=>true
:add_pr_wo_labels=>true
:pulls=>true
:filter_issues_by_milestone=>true
:issues_of_open_milestones=>true
:author=>true
:unreleased=>true
:unreleased_label=>"Unreleased"
:compare_link=>true
:exclude_labels=>["duplicate", "question", "invalid", "wontfix", "Duplicate", "Question", "Invalid", "Wontfix", "Meta: Exclude From Changelog"]
:summary_labels=>["Release summary", "release-summary", "Summary", "summary"]
:breaking_labels=>["backwards-incompatible", "Backwards incompatible", "breaking"]
:enhancement_labels=>["enhancement", "Enhancement", "Type: Enhancement"]
:bug_labels=>["bug", "Bug", "Type: Bug"]
:deprecated_labels=>["deprecated", "Deprecated", "Type: Deprecated"]
:removed_labels=>["removed", "Removed", "Type: Removed"]
:security_labels=>["security", "Security", "Type: Security"]
:configure_sections=>{}
:add_sections=>{}
:issue_line_labels=>[]
:max_issues=>nil
:simple_list=>false
:ssl_ca_file=>nil
:verbose=>true
:header=>"# Changelog"
:merge_prefix=>"**Merged pull requests:**"
:issue_prefix=>"**Closed issues:**"
:summary_prefix=>""
:breaking_prefix=>"**Breaking changes:**"
:enhancement_prefix=>"**Implemented enhancements:**"
:bug_prefix=>"**Fixed bugs:**"
:deprecated_prefix=>"**Deprecated:**"
:removed_prefix=>"**Removed:**"
:security_prefix=>"**Security fixes:**"
:http_cache=>true
:require=>[]
:config_file=>".github_changelog_generator"
:user=>"codeigniter4"
:project=>"codeigniter4"
:since_tag=>"v4.1.4"
:future_release=>"v4.1.5"
:token=>"hidden value"

WARNING: `Faraday::Connection#authorization` is deprecated; it will be removed in version 2.0.
While initializing your connection, use `#request(:authorization, ...)` instead.
See https://lostisland.github.io/faraday/middleware/authentication for more usage info.
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[MGatner]

Rebased with the batch PR from @kenjis