Provide deprecation message for webviz-ert

[andreas-el]

Issue
Resolves #12582

Approach
Added colourful message
Added logging statement to measure usage of webviz-ert and/or the message being shown

Verified using bash and csh, and locally on TGX.

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[andreas-el]

Provided release note for upcoming release;
https://github.com/equinor/scout/issues/1400#issue-3747154188

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.55%. Comparing base (e212883) to head (483cc94).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/ert/__main__.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12584      +/-   ##
==========================================
- Coverage   90.58%   90.55%   -0.03%     
==========================================
  Files         435      435              
  Lines       29933    29938       +5     
==========================================
- Hits        27114    27110       -4     
- Misses       2819     2828       +9     

Flag	Coverage Δ
cli-tests	37.34% <0.00%> (-0.01%)	⬇️
gui-tests	68.64% <0.00%> (-0.05%)	⬇️
performance-and-unit-tests	73.91% <0.00%> (-0.03%)	⬇️
test	38.10% <0.00%> (-0.01%)	⬇️

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[codspeed-hq]

CodSpeed Performance Report

Merging #12584 will not alter performance

_{Comparing andreas-el:deprecate_webviz-ert (483cc94) with main (e212883)}

Summary

✅ 22 untouched

[yngve-sk]

LGTM!

[andreas-el]

Removed the warnings in webviz-ert in this PR equinor/webviz-ert#504