Clarify docs on JNDI properties in Servlet environment

[arend-von-reinersdorff]

• Clarified that JndiPropertySource is always enabled. Previous statement "can optionally enable" might have been before Register JndiPropertySource by default in StandardServletEnvironment [SPR-8545] #13189
• Mentioned global off switch JndiLocatorDelegate.IGNORE_JNDI_PROPERTY_NAME in StandardServletEnvironment

[snicoll]

Thanks again @arend-von-reinersdorff

[arend-von-reinersdorff]

Thanks for merging @snicoll :-)

You restored the word "including" in this phrase:

is populated with additional default property sources including servlet config, servlet context parameters, and a JndiPropertySource

I find "including" a bit misleading: It sounds like more than the 3 mentioned property sources could be added by StandardServletEnvironment. But this is not the case.