Add another option to provide auth details

[drohit-cb]

Description Of Change

Add an option to initialize client with the api key name and private key instead of completely relying on api-key file.

This PR will enable these 2 styles of interacting with the API and make option 1 as the default in our examples and README.

Option 1: Requires client initialize to pass the details such as API key name and private key.

const apiKeyName: string = 'your-api-key-name';
const apiPrivateKey: string = 'your-api-private-key';

const client = new StakingClient(apiKeyName, apiPrivateKey);

client.Ethereum.stake(network, stakerAddress, amount);

Option 2: Need a api key of name .coinbase_cloud_api_key.json present in the root dir.

const client = new StakingClient();

client.Ethereum.stake(network, stakerAddress, amount);

Testing Procedure

Manually ran through the README to execute and make sure all is good.

[drohit-cb]

what would be really cool and nice to have is a "test" API key that perhaps has limited scopes etc that I can plaster in all examples. Could be easy for someone wanting to just run the example as is, without going to the platform.

[ProfMoo]

I really like how the examples don't assume the user placed the API Key at a specific location anymore. It's best to be explicit in the code where possible. However, I do think it's a bit more cumbersome for a user to manually copy/paste the key's two fields into the example (including a private key, which isn't ideal from a security perspective). Especially since the CDP GUI downloads the key onto the filesystem already.

What if we asked the user to specify the file location of the API Key? So maybe it looks like this?

const apiKeyLocation: string = './.coinbase_cloud_api_key.json';

const client = new StakingClient(apiKeyLocation);

This is just an idea, so curious what you think.

[drohit-cb]

It depends what we are trying to do here - something I probably failed calling out in the PR description.. you're right downloading an API key or copy/pasting these 2 values feel equally difficult - it felt like exchanging one problem with perhaps a bigger one 😅 . But the primary aim of moving to coy/pasting these 2 details - key name and private key is so that:

1. We can move away from the coinbase_cloud api key file naming that the platform might take some time to update. We can skip the name confusion if we just copy/paste the relevant fields which the platform offers a good way of copy/pasting.

2. I believe the platform team is working on a token based auth model at which point in time, copy/pasting a token from platform UI will be the expected path. So this PR in a way preps for that eventual future. @deangalvin-cb can maybe confirm/deny this or add more color.

[deangalvin-cb]

👍 Yes, we are working directly with the https://github.com/coinbase/coinbase-sdk-ruby team to see if we can better align & unify our designs. I had @drohit-cb go this route as to not spend too much time building each iteration, and just making this quick improvement now.

[ProfMoo]

Kk I'm onboard 👍

[ProfMoo]

I think we can use fewer words here 🤔.

Suggested change

	3. Get your API keys info such as api key name and api private key from here: https://portal.cdp.coinbase.com/access/api. <br>
	These will be used in order to set up our client later in the example code. <br>
	For detailed instructions refer to our api key setup guide [here](https://docs.cdp.coinbase.com/developer-platform/docs/cdp-keys).
	4. Copy and paste one of the code samples below or any of our [provided examples](./examples/) into an `example.ts` file and run it with `ts-node` :rocket:
	3. Download an API Key from the [portal](https://portal.cdp.coinbase.com/access/api). For more information about API Keys, refer to [our docs](https://docs.cdp.coinbase.com/developer-platform/docs/cdp-keys).
	4. Copy one of the code samples below into an `example.ts` file and run: :rocket:

[drohit-cb]

tl;dr want to move away from downloading the file completely