Input variables on all keys

[wolflu05]

This PR allows the usage of input variables on all fields. It also refactored the template syntax to use jinja2 templates which offer way more functionality than pythons .format(...) function.

⚠️ Breaking

This PR changes the bulk creation syntax in a breaking way.

1. Arguments for generators are now wrapped in round brackets, *NUMERIC{count=1} ==> *NUMERIC(count=1)
2. Accessing variables now need double curly brackets instead of single one, {dim.1} ==> {{dim.1}} (This change is due to the integration if the Jinja2 templating engine)

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Todo

• [x] adjust documentation and add link to Jinja2 template designer docs
• [x] add tests
• [x] input doesn't get loaded into SchemaBuilder
• [x] add jinja2 to dependencies
• [x] rethink templating syntax and maybe adjust generator arguments

fixes #10

[github-actions[bot]]

Coverage Report

	Name	Stmts	Miss	Cover	Missing
inventree_bulk_plugin/BulkGenerator/BulkGenerator.py	94	0	100%
inventree_bulk_plugin/BulkGenerator/dimensions.py	66	0	100%
inventree_bulk_plugin/BulkGenerator/generators/gen_alpha.py	36	0	100%
inventree_bulk_plugin/BulkGenerator/generators/gen_numeric.py	14	0	100%
inventree_bulk_plugin/BulkGenerator/generators/generator.py	33	0	100%
inventree_bulk_plugin/BulkGenerator/template.py	10	0	100%
inventree_bulk_plugin/BulkGenerator/utils.py	2	0	100%
inventree_bulk_plugin/BulkGenerator/validations.py	57	0	100%
inventree_bulk_plugin/InvenTreeBulkPlugin.py	118	0	100%
inventree_bulk_plugin/migrations/0001_initial.py	6	0	100%
inventree_bulk_plugin/models.py	21	0	100%
inventree_bulk_plugin/version.py	1	0	100%
TOTAL	458	0	100%