feat: regex matching for scaler requirements

[jamesstocktonj1]

Feature or Problem

This features allows for scaler configurations to match a regex expression rather than the exact label value. All spread requirements will now be treated as regex with (most) existing wadm files being backwards compatible in matching the labels. This gives more flexible deployment and can be used in addition to leaf nodes to keep traffic within the same area.

Related Issues

• [FEATURE]: Add regex matching to spreadscalers #419

Consumer Impact

• escape characters may need to be used with hosts which contain regex-specific characters (e.g. *, +, ? ...). For example to match the label star-* you would need the regex star-\*

Unit Test(s)

• existing unit tests remain untouched to ensure backwards compatability
• additional unit tests for both component and provider
• additional e2e test for regex matching
• additional serialisation and deserialisation tests

Manual Verification

• various wadm files tested on a simple 4 host setup

[brooksmtownsend]

Hey @jamesstocktonj1 ! I've been chatting it over with some of the other wadm maintainers, and I think there's a general concern with Regex being implemented as-is here today and how long we could support that feature. I wanted to give you a heads up that we're likely going to ask for a bit of a refactor in this PR so that the Regex functionality can fit more into a model like the Nomad constraint feature, for example:

        - type: spreadscaler
          properties:
            instances: 1
            constraints:
              - operation: "=="
                label: "foo"
                value: "bar"
              - operation: "regex"
                attribute: "${labels.foo}"
                value: ".*"

This would be a holistic improvement to our spread logic and isn't a fault of your PR. I didn't want to request changes just yet because the maintainers need to get together and decide on the right structure before we ask you to change anything, but I wanted to give you an update. Do you have any thoughts/concerns/questions for right now?

Thank you so much for taking the initiative to implement this + add tests to verify that it works, this is really a fantastic contribution.