Add information about accessing TypoScript in extension

[sypets]

AFAIK, this information is currently missing. Information about how to access TypoScript can be added, similar to the information on the Flexform page.

todos

• Access TypoScript from Extbase controllers
• Access TypoScript from Fluid with Extbase controllers
• Access TypoScript with Extbase, but outside of controller (with ConfigurationManager?)
• Access TypoScript outside of Extbase
• Access TypoScript with Fluid, without Extbase

Existing resources in TYPO3 documentation:

• configuration in Extbase extensions (Extbase / Fluid book)
• Extbase TypoScript reference (Extbase / Fluid book)

Existing resources outside of TYPO3 documentation

• FluidTypo nicely explains how the "settings" are used, see point Solution
• Stack Overflow: How to get TYPO3 settings in the utility files?
• access via ConfigurationManager, e.g. https://jainishsenjaliya.wordpress.com/2016/03/13/how-to-access-typoscript-settings-data-in-typo3-extension/

Open questions

• should ConfigurationManager be used (and when?)
• can this always be used? Is it recommended?

$GLOBALS['TSFE']->tmpl->setup['plugin.']['tx_xxxx.']['settings.']['storagePid'];

https://stackoverflow.com/a/59598451/2444812