ENH Allow multiple backtick variables in a single value

[emteknetnz]

#10305

Required for the config update in silverstripe/cwp-core#107

[maxime-rainville]

Can you clarify what's the use case this enables that wasn't possible before ... if only for posterity.

This also looks like something that should be documented in the changelog and/or doc?

[emteknetnz]

Required so that we can apply this config in the cwp-core PR

- proxy: '`SS_OUTBOUND_PROXY`:`SS_OUTBOUND_PROXY_PORT`'

I've made a small update to the docs

[michalkleiner]

I'll play the devil's advocate here this time...

Should be targetting 4 if it's an enhancement?
If we need it to fix 4.11 release (or CWP 2.11 depending on this in 4.11) it should be called a bugfix for a bug where we would say we expected multiple variables to be evaluated and that wasn't working.

[emteknetnz]

Yes normally I'd do 4, it's just there hasn't been stable tag on 4.11 yet, only 4.11.0-beta1. So it's correct to target 4.11 here so it will be released as 4.11.0

This is ultimately to fix an issue that was spotted during beta regression testing

[GuySartorelli]

What's the expected behaviour if someone has config that looks like '`something`somethingelse`'?
I'm pretty sure the current regex will substitute the first "something" but not the "somethingelse" which is fine, just want to make sure what is happening is what is expected.

[GuySartorelli]

The actual functionality looks good. Just some additional test cases to catch edge cases.

[GuySartorelli]

Looks good. Merge on green.
Once merged, kick off the tests again on silverstripe/cwp-core#107