Add first proposal for architecture diagrams

[alljames]

What this PR does / why we need it:
Fixes #405

Special notes for your reviewer:
Discussed in Tarmak meeting that it would be good to have what we have so far merged into the codebase. The way the XML is formatted isn't easily diffable but it'll open and be editable using draw.io on any machine

Release note:

Documentation: Add architecture diagrams

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[jetstack-bot]

@alljames: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
tarmak-puppet-module-tarmak-acceptance-1-14-centos	85ba742	link	/test puppet-tarmak-acceptance-centos v1.14

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