chore: set CONTRACTS_NODE_PATH env variable for e2e tests

[AlexD10S]

Closes #31

As specified in the issue, implemented the flag --contracts-node with the path to the contracts-node binary to be used in the end-to-end (e2e) tests. This will allow pop to set the environment variable for the e2e tests as detailed here: https://use.ink/basics/contract-testing/end-to-end-e2e-testing

pop test contract  -p ./my_contract --features e2e-tests -n /Users/bruno/src/substrate-contracts-node/target/debug/substrate-contracts-node

[codecov]

Codecov Report

Attention: Patch coverage is 68.29268% with 13 lines in your changes missing coverage. Please review.

Project coverage is 70.05%. Comparing base (e95c42b) to head (a5ea458).
Report is 1 commits behind head on main.

@@            Coverage Diff             @@
##             main     #209      +/-   ##
==========================================
+ Coverage   68.55%   70.05%   +1.49%     
==========================================
  Files          44       44              
  Lines        6374     6596     +222     
  Branches     6374     6596     +222     
==========================================
+ Hits         4370     4621     +251     
+ Misses       1337     1236     -101     
- Partials      667      739      +72     

Files	Coverage Δ
crates/pop-cli/src/commands/test/contract.rs	0.00% <0.00%> (ø)
crates/pop-contracts/src/test.rs	75.92% <71.79%> (+75.92%)	⬆️

... and 7 files with indirect coverage changes

[Daanvdplas]

• If I do pop test contract --features --help it doesn't display me which features there are. Would be nice it this could be provided.

[AlexD10S]

• If I do pop test contract --features --help it doesn't display me which features there are. Would be nice it this could be provided.

I noticed that too. I was unsure about including it in this PR, but based on your comment, it makes sense to fix it now.

[Daanvdplas]

LGTM!

[evilrobot-01]

General observations.

[evilrobot-01]

Just one item in the docs which I think was missed after the arg rename.

[evilrobot-01]

LGTM!