chore: add increment API

[poppoerika]

Added increment API along with tests to check:

• if increments from 0 to expected amount with string field
• if increments from 0 to expected amount with bytes field
• if increments with setting and resetting field

Closes #304

[cprice404]

🙈 other than I would like a test that covers a negative amount. Also, CI is red.

And I'm not really well versed with our go sdk so you should get Ellery and/or Pete to do final sign-off.

[cprice404]

you should add a test that covers a negative value for amount.

[poppoerika]

I have it here for a string field and here for a bytes field.

Is it better if I take them out and make a separate test for a negative amount for easy readability?

[pgautier404]

I'm happy with this when @cprice404 is, but we need to figure out these test failures. If we've switched to V1 tokens for testing, I would expect these to fail and the tests need to be modified. Using legacy tokens, the credential provider's getAuthToken method returns the auth token it was originally constructed with. For V1 tokens, however, getAuthToken returns an api token extracted from the original, so they are no longer expected to match as the tests assert.