Feat(eos_cli_config_gen): Add support for isis spf-interval hold timer.

[Shivani-gslab]

Change Summary

Add support for isis spf-interval hold timer and interval_unit.

Related Issue(s)

Fixes #3756

Component(s) name

arista.avd.eos_cli_config_gen

Proposed changes

Inserting hold_timer and interval_unit in router_isis.spf_interval

router_isis:
    spf_interval:
        interval_unit: <str; "seconds" | "milliseconds"; default="seconds">
        hold_interval: <int; 1-300000> 

How to test

Test with the molecule scenario added in this PR and test the config on EOS CLI.

Checklist

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)

[MaheshGSLAB]

LGTM, tested on lab

[ClausHolbechArista]

The names of the keys are slightly misleading.
Currently they are <interval> <wait_interval> <hold_interval>
From the help texts given above it seems like they should be <wait_interval> <initial_wait_interval> <hold_interval>. Maybe check show cli commands and the EOS manual to clear this up.
Nevermind. This Pr is only adding the hold_interval, so keep that :)