[Mohith26]

Closes #1121

Adds Jinja's {% with %}...{% endwith %} scoped assignment tag. Right now this fails with Unknown tag: with:

{% with jobname="my_job", schedule="0 1 * * 0", deadline=300 %}
  {% include 'objects/CronJob.jinja.yml' %}
{% endwith %}

Behavior follows Jinja:

• names assigned by the tag, and anything set inside the block, are gone after endwith, and outer variables with the same name come back
• every value is evaluated in the enclosing scope before any name is bound, so {% with a = 1, b = a %} gives b the outer a
• {% with %} with no assignments just opens a scope

How it works: WithTag splits the assignments on top-level commas (commas and = inside strings, brackets and comparisons like ==/<= are left alone), enters a scope, runs a multi-target set ({% set a, b = x, y %}) through the registered set tag, then renders the body. Going through set means eager execution gets the existing deferred-assignment handling. EagerWithTag renders the block in a child context and, if anything stayed deferred, wraps the output with wrapInChildScope the same way EagerForTag does:

{% with a = deferred, b = 2 %}{{ a }} {{ b }}{% endwith %}
->
{% for __ignored__ in [0] %}{% set a, b = deferred, 2 %}{{ a }} {{ b }}{% endfor %}

If set is disabled in the config, a with that assigns adds a DISABLED error and renders nothing (a bare {% with %} still works), so it can't be used to get around a disabled set tag.

Tests:

• WithTagTest: scoping, shadowing, outer-scope evaluation, nesting, loop variables, commas/operators inside values, the example from the issue, and syntax errors (bad target, missing =, missing value, duplicate names)
• EagerWithTagTest: runs all of the above in eager mode, plus deferred cases that render the eager output a second time and check the final result
• WithTagDisabledSetTest: default and eager mode

mvn verify passes locally (2272 tests, plus checkstyle/pmd/spotbugs/spotless). Note that the checked-in wrapper is Maven 3.6.2, but git-commit-id-maven-plugin 9 needs 3.6.3+, so I ran it with Maven 3.9.9.