feat: add `tensorboards-web-app` rock for CKF 1.9 #98

Job	Run time
Get rocks modified and build-scan-test them / Get rockcraft paths modified / Get all rockcraft.yaml paths	3s
Get rocks modified and build-scan-test them / Get rockcraft paths modified / Get paths for ROCKs modified by PR	2s
Get rocks modified and build-scan-test them / build-scan-test-publish-rock (tensorboards-web-app) / build / Build tensorboards-web-app	7m 20s
Get rocks modified and build-scan-test them / build-scan-test-publish-rock (tensorboards-web-app) / sanity-tests / Sanity test tensorboards-web-app:1.9.0	53s
Get rocks modified and build-scan-test them / build-scan-test-publish-rock (tensorboards-web-app) / scan / Scan tensorboards-web-app:1.9.0	1m 55s
Get rocks modified and build-scan-test them / build-scan-test-publish-rock (tensorboards-web-app) / integration-tests / Test tensorboards-web-app:1.9.0	6m 17s
Get rocks modified and build-scan-test them / build-scan-test-publish-rock (tensorboards-web-app) / publish	0s
	16m 30s

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