Use environment variables to initialize client and server

[shubham1172]

Description

This PR makes DaprClient and DaprServer configurable using environment variables. If missing, they fallback to a sane default value.

Issue reference

Please reference the issue this PR will close: #178

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[shubham1172]

/cc @XavierGeerinck for review

[XavierGeerinck]

One extra question: I see you are using ?? is there a reason you are not using ||?

I personally prefer || more since it also replaces null values in Javascript, since Javascript is sometimes "interesting" with "Falsey" variables

[shubham1172]

@XavierGeerinck, I had seen ?? in other TS codebases. Also saw this one https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#nullish-coalescing

From https://stackoverflow.com/questions/61480993/when-should-i-use-nullish-coalescing-vs-logical-or, ||

But the OR operator || can be problematic if your left value might contain "" or 0 or false

What do you think?

[XavierGeerinck]

Awesome, LGTM