fix: slot stats are not filled in everywhere

[hamidzr]

Description

I added a summary of slots to the agent responses and annotated it as always available resulting the generated client code to expect that in some other apis I did not update.

issue was caught before being released

Test Plan

ee run with this cherry-picked https://app.circleci.com/pipelines/github/determined-ai/determined-ee/11396/workflows/aff838c6-3eff-49cc-9d2f-8735bbd04ee2/jobs/571167

call various endpoints getting the Agent object

proto/src/determined/api/v1/api.proto
284:  rpc GetAgents(GetAgentsRequest) returns (GetAgentsResponse) {
293:  rpc GetAgent(GetAgentRequest) returns (GetAgentResponse) {
320:  rpc EnableAgent(EnableAgentRequest) returns (EnableAgentResponse) {
329:  rpc DisableAgent(DisableAgentRequest) returns (DisableAgentResponse) {

hbp ➜ d/determined git:(main) det dev b call get_GetAgent agent1 > /dev/null
Usage: get_GetAgent <= agentId: str

'NoneType' object is not subscriptable
hbp ➜ d/determined git:(main) gco -
Switched to branch 'hz-slot-stats-can-be-null'
Your branch is up to date with 'origin/hz-slot-stats-can-be-null'.
hbp ➜ d/determined git:(hz-slot-stats-can-be-null) det dev b call get_GetAgent agent1 > /dev/null
hbp ➜ d/determined git:(hz-slot-stats-can-be-null)

Commentary (optional)

https://hpe-aiatscale.slack.com/archives/C04C9JXB1C2/p1711646351359479

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 31 lines in your changes are missing coverage. Please review.

Project coverage is 47.13%. Comparing base (1e45918) to head (78bac61).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9070      +/-   ##
==========================================
- Coverage   47.15%   47.13%   -0.03%     
==========================================
  Files        1152     1152              
  Lines      141866   141866              
  Branches     2416     2414       -2     
==========================================
- Hits        66899    66867      -32     
- Misses      74777    74809      +32     
  Partials      190      190              

Flag	Coverage Δ
backend	42.92% <0.00%> (-0.08%)	⬇️
harness	64.31% <ø> (ø)
web	38.92% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
master/internal/api_agents.go	0.00% <ø> (-21.59%)	⬇️
master/pkg/model/agent.go	0.00% <0.00%> (ø)

... and 4 files with indirect coverage changes

[stoksc]

lgtm