Prepare for release v1.9.8

[aanm]

Summary of Changes

Minor Changes:

• Update k8s libraries to 1.19.11 (k8s: Update k8s libraries to 1.19.11 #16248, @nathanjsweet)
• helm: add back 'wellKnownIdentities' (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR helm: add back 'wellKnownIdentities' #16142, @bmcustodio)

Bugfixes:

• daemon: Ignore cilium_* interfaces when deriving NodePort device (Backport PR v1.9 backports 2021-05-21 #16270, Upstream PR daemon: Ignore cilium_* interfaces when deriving NodePort device #16104, @eyanulis)
• Fixed bug causing policy realization being skipped in some scenarios with endpoint identity churn. (Backport PR v1.9 backports 2021-05-27 #16339, Upstream PR endpoint: Skip waiting-to-regenerate -> waiting-for-identity state transitions #16271, @jrajahalme)
• Ignore K8s namespace events that have the same labels (Backport PR v1.9 backports 2021-05-27 #16339, Upstream PR pkg/k8s: ignore namespace events that do not change labels #16268, @aanm)
• loader: Revert incorrect initialization of endpoints in chaining mode (Backport PR v1.9 backports 2021-05-27 #16339, Upstream PR loader: Revert incorrect initialization of endpoints in chaining mode #16227, @pchaigno)

CI Changes:

• ci: add slack notification to GH actions (Backport PR v1.9 backports 2021-05-21 #16270, Upstream PR ci: add slack notification to GH actions #16218, @nebril)
• examples, connectivity-check, test: Use even-numbered nodePort (Backport PR v1.9 backports 2021-05-21 #16270, Upstream PR examples, connectivity-check, test: Use even-numbered nodePort #16158, @christarazi)
• Improve ipsec compile-time testing in CI (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR Improve ipsec compile-time testing in CI #15872, @joestringer)
• node-neigh: Fix unit test flake (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR node-neigh: Fix unit test flake #16072, @brb)
• test: add e2e tests for fromEntities: cluster and all (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR test: add e2e tests for fromEntities: cluster and all #15398, @chez-shanpu)
• test: Extend coverage for host policies enforcement (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR test: Extend coverage for host policies enforcement #14822, @pchaigno)
• test: Fix the search for VIPs in cilium service list (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR test: Fix the search for VIPs in cilium service list #15968, @pchaigno)
• test: Mark GKE CI pipeline as running Linux 4.19 (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR test: Mark GKE CI pipeline as running Linux 4.19 #14639, @pchaigno)
• test: Misc improvements (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR test: Misc improvements #16064, @pchaigno)

Misc Changes:

• contrib: Make upstream commit check more generic (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR contrib: Make upstream commit check more generic #16160, @joestringer)
• docs, gsg: add link to plumbers talk on service lb mechanisms (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR docs, gsg: add link to plumbers talk on service lb mechanisms #16171, @borkmann)
• docs, gsg: minor edits to kpr guide and note on hybrid use (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR docs, gsg: minor edits to kpr guide and note on hybrid use #16169, @borkmann)
• docs: gsg/operations - use parsed-literal for all blocks referring SCM_WEB (Backport PR v1.9 backports 2021-05-17 #16173, Upstream PR docs: gsg/operations - use parsed-literal for all blocks referring SCM_WEB #15963, @ti-mo)
• docs: add ids to the list of special identities (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR docs: add ids to the list of special identities #16123, @bmcustodio)
• docs: add information about ConfigMap updates (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR docs: add information about ConfigMap updates #16141, @aanm)
• docs: Clarify coordination for backporting process (Backport PR v1.9 backports 2021-05-21 #16270, Upstream PR docs: Clarify coordination for backporting process #15989, @christarazi)
• Improve author attribution scripts (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR Improve author attribution scripts #15899, @joestringer)
• Specify scrape interval for Hubble metrics (Backport PR v1.9 backports 2021-05-19 #16224, Upstream PR Specify scrape interval for Hubble metrics #16214, @christian-2)

Other Changes:

• install: Update image digests for v1.9.7 (install: Update image digests for v1.9.7 #16133, @joestringer)
• v1.9: Revert broken tests (v1.9: Revert broken tests #16333, @twpayne)