Feature/ioc boot

[BenBradnick]

This PR contains a set of small changes based on generating the ioc boot script:

1. Update docs to reflect ibek build-helm no longer needs a schema arg
2. Added 2 elements to the IOC boot script - environment variables and pos iocInit entries. An epics.ibek.yaml file was created with entities which have entries for these new elements, as well as a test for generating a boot script containing them
3. Tidied up the existing ioc boot Jinja template to remove duplicates and improve spacing
4. Fixed test in test_cli for building IOC against multiple support module definition files

[gilesknap]

This looks great.

[gilesknap]

I like epics.ibek.yaml.

There are probably other things that would go in here I'm guessing.

[thomascobb]

I've never seen this syntax before, what does it do?

[BenBradnick]

It's syntax for control structures, in this case I just check to see if env_var_elements is defined - https://jinja.palletsprojects.com/en/3.0.x/templates/#list-of-control-structures

This was just to keep the boot script tidy, as I found it difficult to control new lines with optional elements.