Add more Exception messages for Config.getValue()

[Joseph-Cass]

Partly addresses #485
In particular, resolves:

• More detailed Error messages #485 (comment)
• More detailed Error messages #485 (comment)

Under the current implementation all of the tests from ConfigValueConversionRulesExceptionsTest.java would have thrown

Property %s is required but the value was not found or is empty

Except from badConversion() which would have thrown:

Expected an integer value, got "notInt"

[radcortez]

@Joseph-Cass Is this ready?

[Joseph-Cass]

This comment may change depending on the outcome of this discussion, but other than that, I'm happy if you are :)

[Joseph-Cass]

Does this look okay to you @radcortez ?

[radcortez]

Yes! Thank you!

[radcortez]

Cannot backport to 1.x due to merge conflicts. Please backport manually:
Run:

git clone https://github.com/smallrye/smallrye-config.git
git fetch origin pull/504/head:pr-504
git checkout -b 1.x origin/1.x
git checkout -b backport-#504-to-1.x
# One or more of the following command will fail, you will need to fix the conflict manually
git cherry-pick ed53f84b2ba931cb9b217f1dc61373fb37465c45
git cherry-pick d091ce36e7784cec833058328684330848e4e5a2
git cherry-pick ac2c83fe02dea7543bca7e2b42e0830bd09f2370
# Once all commits have been cherry-picked:
git push --set-upstream origin backport-#504-to-1.x

To fix the conflict, first check which file is impacted using: git status
For each file with a resolved conflict, execute: git add $FILE
Then, commit the files using the same commit message as the original commit: git commit -m "..."

Once done and pushed, open the pull request.

• Title: [1.x] Backport Add more Exception messages for Config.getValue()
• Message: Backport Add more Exception messages for Config.getValue() #504 to 1.x.
• ⚡ Set the target branch to 1.x
• Set the milestone and the labels if needed

[Joseph-Cass]

@radcortez I'm not sure this PR is suitable for 1.x. It updates error messages related to "empty" and null behaviour which changed in the spec between MP Config 1.x -> 2.0?

[radcortez]

Ahah, I was actually using this as a test for a script I wrote to do backports.

There are some interesting things that I would like to backport, but I haven't really tried it yet.