Update Action for Use on GitHub Enterprise

Currently the action doesn't seem to be useable for Workflows running on GitHub Enterprise. This is because:

1. getVersion() relies on Oktokit defaulting the baseUrl. In Enterprise, this baseUrl appears to be defaulted to the enterprise URL rather than public GitHub.
2. The GitHub token provided by a Workflow may not be able to authenticate with the GitHub API on https://api.github.com/ if it limited by scope - this is needed by getVersion()
3. The token needed by setUpTool() may therefore need to be different from the token used by getVersion().

Proposed changes:

1. Hardcode the GitHub API URL to get releases by tag so it doesn't default to the Enterprise URL
2. Add an additional Action input to set a different token used by the setUpTool function to set Allure job metadata. This is defaulted to ${{ github.token }} to avoid regressions.

Enabling use on github enterprise

d543d2d

Updating readme

3373f27

All committers have signed the CLA.