[Functions] Add CI

[pragnagopa]

CI was added microsoft/azure-maven-plugins#425 as part of maven plugin. It should be moved here

[pragnagopa]

cc @jdneo, @Flanker32

[jdneo]

The idea is correct, but why considering it as GA must have?

[pragnagopa]

cc: @brunoborges @selvasingh @paulbatum - FYI as this has come up multiple times
Ideally we should have had the CI setup from the beginning. It is nearly impossible to catch regressions between various components without CI.
This is even more important once we GA as it will be too late to wait for azure-functions-java-library changes to be published to maven before archetype consumes it.

Apart from all the reasons why we need it, we already have automation build scripts, here is a sample for updating the versions to the ones CI needs to test https://github.com/Azure/azure-functions-java-library/pull/60/files#diff-e3ae12ee6afa1aa9ef6e708438cb1663

[pragnagopa]

@Flanker32 / @jdneo - Right now there is no way to verify changes in the PR #79 I have verified it manually.
I have updated the label to "javafunctions-v2-GA-shouldhave" as this is not GA blocker.
Please consider adding CI here soon.

[asavaritayal]

/cc @selvasingh