Added imagemagick-heic and updated readme

[homerr]

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• [x] I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Added the imagemagick-heic modele and added details of config changes required

Benefits of this PR and context:

Should close issue #421

How Has This Been Tested?

Spun up test image, added some heic files, tested with config.php changes and found working

Source / References:

[LinuxServer-CI]

I am a bot, here are the test results for this PR: https://ci-tests.linuxserver.io/lspipepr/nextcloud/28.0.4-pkg-135803c5-dev-5905985884c102f492b0055fdf57303d69575173-pr-424/index.html https://ci-tests.linuxserver.io/lspipepr/nextcloud/28.0.4-pkg-135803c5-dev-5905985884c102f492b0055fdf57303d69575173-pr-424/shellcheck-result.xml	Tag	Passed
amd64-28.0.4-pkg-135803c5-dev-5905985884c102f492b0055fdf57303d69575173-pr-424	✅
arm64v8-28.0.4-pkg-135803c5-dev-5905985884c102f492b0055fdf57303d69575173-pr-424	✅

[LinuxServer-CI]

I am a bot, here are the test results for this PR: https://ci-tests.linuxserver.io/lspipepr/nextcloud/28.0.4-pkg-135803c5-dev-c9de3ee13ffc572062e2571ea81fc03bc9218d66-pr-424/index.html https://ci-tests.linuxserver.io/lspipepr/nextcloud/28.0.4-pkg-135803c5-dev-c9de3ee13ffc572062e2571ea81fc03bc9218d66-pr-424/shellcheck-result.xml	Tag	Passed
amd64-28.0.4-pkg-135803c5-dev-c9de3ee13ffc572062e2571ea81fc03bc9218d66-pr-424	✅
arm64v8-28.0.4-pkg-135803c5-dev-c9de3ee13ffc572062e2571ea81fc03bc9218d66-pr-424	✅