Continuation of rebased #311.

Necessary changes:

• Fix translated labels as reported by @msollmann
• implement cObject for inject ()
• localization for custom items
• update tests
• fix acceptance tests for custom theme
• update documentation: TypoScript paths
• update documentation: translations
• update documentation: upgrade v2 -> v3 (templates)
• update documentation: asset paths: point to https://docs.typo3.org/m/typo3/guide-installation/main/en-us/MigrateToComposer/AssetMigration.html#migrate-public-assets

Asset paths in TypoScript

_asset paths in TypoScript can be added with

  inject.insertData = 1
  inject = <script src="/{path : EXT:....}">

(mind the leading /!)
but this has shortcomings (see https://forge.typo3.org/issues/99203#change-507069). For v13 we'll get the {asset : ...} getText (https://review.typo3.org/c/Packages/TYPO3.CMS/+/77018).

f:translate in non-Extbase contexts

Due to a probable requirement for extensionName in each {f:translate} instance (forge issue: https://forge.typo3.org/issues/102315) it is very probable that custom templates will break. That would warrant a major (breaking) release for cookieman.

Translations in TypoScript (solved in TYPO3 Core v12.4.9+)

Adding translations with plugin.*._LOCAL_LANG in page layout context did also not work anymore in TYPO3v12 (https://forge.typo3.org/issues/100759) - (This is solved for v12.4.9+ by https://review.typo3.org/c/Packages/TYPO3.CMS/+/82023)

We might have to recommend this instead:

# @see https://docs.typo3.org/m/typo3/reference-coreapi/12.4/en-us/ApiOverview/Localization/ManagingTranslations.html#custom-translations
$GLOBALS['TYPO3_CONF_VARS']['SYS']['locallangXMLOverride']['EXT:cookieman/Resources/Private/Language/locallang.xlf'][]
        = 'EXT:configure_cookieman/Resources/Private/Language/locallang_cookieman.xlf';
$GLOBALS['TYPO3_CONF_VARS']['SYS']['locallangXMLOverride']['de']['EXT:cookieman/Resources/Private/Language/locallang.xlf'][]
        = 'EXT:configure_cookieman/Resources/Private/Language/de.locallang_cookieman.xlf';

How to use this:

composer req dmind/cookieman:dev-dev/12lts (or, pin a commit when using it in production: for example dmind/cookieman:dev-dev/12lts#cc9364f4ba76de706f4af2a3e1be7372aaabba09)
– please test and give feedback

Fixes: #304
Fixes: #271