Fix: check healthcheck and heartbeat after ExApp container start

[bigcat88]

After the previous PR(#430) which added stopping application containers feature when shutting down, as @andrey18106 correctly noted during our 1:1 conversation:

we cannot rely on the application inside the docker container to be ready to process the request at the moment the docker container is turned on.

This PR introduces handling of it by checking health-check and heartbeat.

[bigcat88]

/backport stable30

[bigcat88]

/backport to stable30

[backportbot[bot]]

The backport to stable30 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable30
git pull origin stable30

# Create the new backport branch
git checkout -b backport/436/stable30

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 7360d998

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/436/stable30

Error: Failed to cherry pick commits: error: no cherry-pick or revert in progress fatal: cherry-pick failed

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[bigcat88]

/backport to stable29

[backportbot[bot]]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/436/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 7360d998

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/436/stable29

Error: Failed to cherry pick commits: error: no cherry-pick or revert in progress fatal: cherry-pick failed

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.