Add a configurable BASE_URL to allow Amundsen to be served outside of the root URL

[dmateusp]

Summary of Changes

Full description of the issue: amundsen-io/amundsen#424

On the Python (Flask) side, I leveraged url_for in index.html, a BASE_URL configuration variable and a middleware class. I also took the routes defined in amundsen_application/api/__init__.py and standardized them by using the same Blueprints mechanism as the rest was using.

On the Javascript side, I added an importable axios instance to inject the BASE_URL into the calls. Note that I have very little experience on front-end, I got some help from @rebeccarich at Earnest but I realized there's many things I don't understand there. For example I try to get the environment variable here, but I imagine it's not getting picked up because it's client-side ? Any feedback on which way we should do this?

On the scss side, I'm injecting the variable, but in this case it's done at compile time as far as I understand, which is undesirable (we probably don't want people building Amundsen themselves everytime they need BASE_URL to be set), also not sure about the right way of doing it

Happy to get initial feedback

Tests

Updates the tests to use the new axios

Documentation

TODO: add docs

CheckList

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• PR title addresses the issue accurately and concisely. Example: "Updates the version of Flask to v1.0.2"
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• PR adds unit tests, updates existing unit tests, OR documents why no test additions or modifications are needed.
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  • All the public python functions and the classes in the PR contain docstrings that explain what it does
• PR passes all tests documented in the developer guide

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.

[ttannis]

@dmateusp please let us know if you intend to move forward with this PR. Thanks!

[dmateusp]

hey @ttannis I'm going to close this PR for now