Update CONTIRBUTING.md for port forwarding and frontend start:dev:ext

[christianvogt]

Description

Add documentation for using frontend script npm run start:dev:ext.
Add documentation for port forwarding services when running a local backend.

How Has This Been Tested?

Test Impact

Request review criteria:

Self checklist (all need to be checked):

• The developer has manually tested the changes and verified that the changes work
• Commits have been squashed into descriptive, self-contained units of work (e.g. 'WIP' and 'Implements feedback' style messages have been removed)
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has added tests or explained why testing cannot be added (unit or cypress tests for related changes)

If you have UI changes:

• Included any necessary screenshots or gifs if it was a UI change.
• Included tags to the UX team if it was a UI/UX change (find relevant UX in the SMEs section).

After the PR is posted & before it merges:

• The developer has tested their solution on a cluster by using the image produced by the PR to main

[lucferbux]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lucferbux

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [lucferbux]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment