fix(blooms): Initialize bloom gateway client only once

[chaudum]

What this PR does / why we need it:

The bloom gateway client is used both in the bloom builder and in the index gateways. When running Loki in SSD mode, both services are part of the backend target, and therefore the client is initialised twice, leading to duplicate metrics registration and a subsequent panic.

This commit extracts the initialisation of the bloom gateway client into a separate service that is started once and becomes a dependency of both bloom builder and index gateway.

Which issue(s) this PR fixes:

Fixes: #14083

[loki-gh-app]

The backport to release-3.3.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-15994-to-release-3.3.x origin/release-3.3.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x e271e22f7c1fae676e2fce6ab002b358694d9450

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-15994-to-release-3.3.x
# Create the PR body template
PR_BODY=$(gh pr view 15994 --json body --template 'Backport e271e22f7c1fae676e2fce6ab002b358694d9450 from #15994{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'fix(blooms): Initialize bloom gateway client only once (backport release-3.3.x)' --body-file - --label 'size/M' --label 'type/bug' --label 'backport' --base release-3.3.x --milestone release-3.3.x --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-15994-to-release-3.3.x

# Create a pull request where the `base` branch is `release-3.3.x` and the `compare`/`head` branch is `backport-15994-to-release-3.3.x`.

# Remove the local backport branch
git switch main
git branch -D backport-15994-to-release-3.3.x

[loki-gh-app]

The backport to release-3.2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-15994-to-release-3.2.x origin/release-3.2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x e271e22f7c1fae676e2fce6ab002b358694d9450

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-15994-to-release-3.2.x
# Create the PR body template
PR_BODY=$(gh pr view 15994 --json body --template 'Backport e271e22f7c1fae676e2fce6ab002b358694d9450 from #15994{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'fix(blooms): Initialize bloom gateway client only once (backport release-3.2.x)' --body-file - --label 'size/M' --label 'type/bug' --label 'backport' --base release-3.2.x --milestone release-3.2.x --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-15994-to-release-3.2.x

# Create a pull request where the `base` branch is `release-3.2.x` and the `compare`/`head` branch is `backport-15994-to-release-3.2.x`.

# Remove the local backport branch
git switch main
git branch -D backport-15994-to-release-3.2.x