#637 feat: implement harness quota

[zsinnema]

Closes #637

Implemented solution: ...

How to test this PR:
read the documentation of the _compute_quotas_from_tree function for setting up an example in Keycloak

from cloudharness.applications import get_configuration
from cloudharness.auth.quota import get_user_quotas

app_config = get_configuration("<the app with quotas>")
user_id = "<the user id to get the quota for>"
print(get_user_quotas(app_config, user_id))

Sanity checks:

• The pull request is explicitly linked to the relevant issue(s)
• The issue is well described: clearly states the problem and the general proposed solution(s)
• From the issue and the current PR it is explicitly stated how to test the current change
• The labels in the issue set the scope and the type of issue (bug, feature, etc.)
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Breaking changes (select one):

• The present changes do not change the preexisting api in any way
• This PR and the issue are tagged as a breaking-change

Possible deployment updates issues (select one):

• There is no reason why deployments based on CloudHarness may break after the current update
• This PR and the issue are tagged as alert:deployment

Test coverage (select one):

• Tests for the relevant cases are included in this pr
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Documentation (select one):

• The documentation has been updated to match the current changes
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Nice to have (if relevant):

• Screenshots of the changes
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